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Grade: 3 Lesson Title: PerimeterUnit: 1 Addition and Subtraction Applications within 100 (Lesson 4 of 4) Time Frame: 3-4 daysEssential Question:

How does How can understanding the relationship between addition and subtraction aid us in problem solving? How does knowing the distance around objects (perimeter) support us in the real world?

Targeted Content Standard(s): Student Friendly Learning Targets3.MD.8 Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.

I can…

Measure perimeters Solve real-world problems involving

perimeter including: Finding the perimeter given the

side lengths Finding an unknown side length

given the perimeter

Targeted Mathematical Practice(s): 1 Make sense of problems and persevere in solving them 2 Reason abstractly and quantitatively 3 Construct viable arguments and critique the reasoning of others 4 Model with mathematics 5 Use appropriate tools strategically 6 Attend to precision 7 Look for and make use of structure 8 Look for an express regularity in repeated reasoning

Supporting Content Standard(s): (optional)2.OA.1 Solve problems involving addition and subtraction within 100 in adding to, taking from, putting together, taking apart and comparing situations within 100.2.NBT.5 Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.2. NBT.6 Add up to four two-digit numbers using strategies based on place value and properties of operations.3.OA.8 Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding.Purpose of the Lesson:Students will develop an understanding the concept of perimeter and solve perimeter problems. Explanation of Rigor: (Fill in those that are appropriate.)Conceptual:Students will understand perimeter as the distance around shapes.

Procedural:Students will find perimeters of polygons by counting, by adding up sides and by measuring using tools.Students will compute missing sides given the perimeter.

Application:Students will solve one- and two-step problems involving perimeter of polygons.

Vocabulary:lengthperimeter

metercentimeter

inchfoot

yardunknown

unit

Evidence of Learning (Assessment):

Pre-Assessment: Measuring Length

Formative Assessment(s): Perimeter with Geoboards Assessment, Finding Perimeter of Polygons, Measuring



Perimeters, Finding Unknown Side Lengths

Summative Assessment: Solving Perimeter Problems

Self-Assessment: Solving Perimeter Problems

Lesson Segments:1. Measuring Length Pre-assessment; Finding perimeter of polygons in real-life situations2. Finding perimeter by counting using manipulatives 3. Modeling and measuring perimeter on geoboards and dot paper 4. Finding perimeter by adding when all sides are given5. Finding perimeter of polygons with one unknown side when reasoning about shape attributes 6. Finding perimeter of polygons with one unknown side when perimeter is given7. Finding perimeter of polygons using measurement tools with real-life objects; Summative Assessment



Lesson Procedures: Segment 1

Approximate Time Frame:

50-60 minutes

Lesson Format: Whole Group Small Group Independent

Modeled Guided Collaborative Assessment

Resources:Pre-Assessment for Measurement Paper/pencilMasking tapeLarge floor area to tape figures for the students to walk aroundWalking the Perimeter

Focus:

Finding the perimeter of a polygon using real-life situations.

Modalities Represented: Concrete/Manipulative Picture/Graph Table/Chart Symbolic Oral/Written Language Real-Life Situation

Math Practice Look For(s):.MP2 Reason abstractly and quantitatively. Students will make sense of the quantities that they find and their relationships within the real-life problem.

MP4 Model with mathematics. Students will walk around a given polygon, make approximations regarding the steps taken and analyze the relationships they find mathematically to draw conclusions.

MP5 Use appropriate tools strategically. Students will use tape diagrams and the basic unit of shoes to measure the distance around shapes that have been taped to the floor.

MP 6 Attend to precision. Students will specify the shoe units they use and will determine what constitutes rounding the steps up 1 unit. The students will also count accurately the number of steps taken to determine the perimeter so correct conclusions can be drawn from the measurements taken.

Differentiation for Remediation: If you have a student that has physical difficulties when walking, assign a helper to complete the walking portion of the activity for the student. The helper will take the child’s shoe and walk it around the shape. The child will count the steps for the helper and give the answer to be recorded.

Differentiation for English Language Learners: If counting numbers in English is difficult, assign a helper to count in English while the ELL student is counting in his/her language. When both finish counting, the answer in number form should be the same, thus comprehension of the amount should be realized.

Differentiation for Enrichment: As an extended activity, the enrichment students can use the perimeter they calculate for each figure and predict what the new perimeter would be if they are doubled or tripled it in size. When sketching the polygon on the worksheet, they should record the new side lengths when doubled or tripled, add the new side lengths together and see whether the doubled and tripled perimeters calculated match their predictions.

Potential Pitfall(s): You must meet in a room that has ample space to tape the shape diagrams to the floor. If too small a space is available, one shape at a time will need to be taped which will extend the time of the lesson.

Independent Practice (Homework):



Administer Pre-Assessment for Measurement (15-20 minutes)

This could be given at another time other than mathematics time.

Teacher Notes/Reflections:

Steps:1. Before the activity begins, students should move their desks

off to the side of the classroom if they can so the teacher can tape polygon figures to the classroom floor. All shapes should be large enough for students to walk heel to toe around the figure so they can count the steps to find the perimeter. Some examples include:

2. Explain that the task today is to solve the perimeters for each polygon shape taped to the floor using the number of steps they take as the basic unit of measure.

3. Demonstrate to the students how to walk heel to toe around the shape. Explain that all steps may not fit perfectly when approaching the end of the side of the shape. In order to provide an appropriate approximation, model to the students using their shoes that if more than half of the shoe will fit when the end of each side is reached, this partial step will count as a whole step. If the partial step’s length is less than half of the student’s shoe, then the partial unit will not be counted at all.

4. In order to complete the activity, students should be placed in groups of three. Using the Walking the Perimeter assessment sheet, students should first sketch the shape taped to the floor. Each student can then walk heel to toe to count the steps for each shape. When the steps have been counted, each student may record the total amount of steps on the assessment sheet for each team member. Step 4 will be repeated for all polygon shapes taped to the floor.

5. When the steps have been calculated for each shape, team members can discuss with their group the answers to the questions below the chart. They should discuss the relationships between the size of the shoe and the number of steps taken.

6. In order to fully embed the idea of why we need to use



perimeter in our lives, questions you may want to ask students can include:

Name a real-life situation when someone would use steps to measure a perimeter? (boundaries of a playing field)

What items might we build that require you to know theperimeter before you order supplies? (fence, landscape bricks, flower borders)

What are possible outcomes if you didn’t measure the perimeter before you began the project? (too many supplies, not enough supplies, money wasted ontoo many supplies ordered)

How does your teacher use perimeter in his/her classroom?(border around the bulletin boards)



Segment 2


80 - 100 minutes (Could be 2 days)



Resources: Rulers Manipulatives: craft sticks, straws,

toothpicks, paper clips, etc. Grid paper. Ralph the Dog sheet. Perimeter with Manipulatives Assessment Observational Checklist

Focus: Finding perimeter by counting (with manipulatives)


Math Practice Look For(s):

MP5 Use appropriate tools strategically. Students will use rulers and number lines to complete the pre-assessment. Students will also utilize physical objects to model perimeter throughout this segment. Grid paper will also be used to sketch figures.

Differentiation for Remediation: Some students may require additional practice in building perimeters. Students may also need assistance creating different figures with same perimeter. More tactile experiences will benefit learning.

Differentiation for English Language Learners: Vocabulary activities focusing on the language of perimeter, around, distance, length, and border.

Differentiation for Enrichment: Some students may be prepared for finding the perimeter or more complex figures.

Potential Pitfall(s):

Some students may have fine motor difficulties. They may have difficulty in placing manipulatives correctly (no overlaps or gaps) or in transferring figure to grid paper.


Step 1:Option: The following activity can be done on a SmartBoard or student creations can be shared on document cameras.Direct students to take a piece of paper and a pencil. Have students place their pencil on the paper and draw a large dot. Tell students to start at the dot and draw anything they want with these conditions:

The line must return to the starting dot. The line may not cross over anything already drawn.

Circulate and observe, giving students time to create images. Allow students to share their images. Unacceptable images: (Discuss why these images do NOT meet above requirements.)

Acceptable images:



Added dimension of drawing image with straight lines only. Discuss acceptable images. (Students may find drawing straight lines challenging. Accept reasonable lines.) (10-15 minutes)

Set up scenario: The family down the street has a new puppy and they want to keep him safe. They are also worried about other animals getting into their yard. They need to build a fence around the puppy for when he is in the backyard.

Pass out Ralph the Dog sheets (allow class to name dog if desired.) Direct students to draw a dot where the fence could begin, and draw a fence around “Ralph.”

Allow students to share drawings.Probe students to determine if any of them know that this is called the “perimeter.” Begin Anchor Chart for perimeter. Continue to include specific topics as lessons continued and as they are introduced. (15-20 minutes)



Step 2:

Ask students for ideas about how one might be able to measure the perimeter, or length of fence, around the puppy. Chart ideas.

Show students these items: craft sticks, straws, toothpicks, paper clips, etc.

Choose one item and guide students in laying down items around the perimeter, counting as you go.

WATCH FOR: Students leaving gaps between items or students overlapping items. (Add these steps to Anchor Chart.)

Repeat with different manipulatives and allow students to share perimeters. Record on the board the various totals using the different items. (20 minutes)


Step 3:

Some students may build different shapes using the same number of items. Guide students to ALL count out 10 toothpicks, thus using the same manipulative, and ask students to create a fence for the puppy.

Pass out grid paper and allow students to sketch their yard.

Circulate and look for two students who have created different figures with the toothpicks.

Allow these students to share their figures or sketches on document camera or recreate on the board.

Ask for other solutions and have those students share.

Add to Anchor Chart as discussion topics arise.

Continue this process for additional totals using different manipulatives (if appropriate): 14, 20, 6.

(20-30 minutes)Step 5: Administer Perimeter with Manipulatives and Grids Assessment Utilize the Observation Checklist to gauge students’ understanding of concepts.

(20 minutes)



Segment 3


60-80 minutes



Resources: Let’s Prove Perimeter worksheet. Geoboards and rubber bands. Straws cut into appropriate sizes

NOTE: Straw pieces must fit between pegs/dots on worksheet/geoboard.

Post-it notes. Perimeter Practice on Geoboards

worksheet. Perimeters with Geoboards

AssessmentFocus:

Modeling and measuring perimeters on geoboards and dot paper.



MP5 Use appropriate tools strategically.

Students will use physical objects to model perimeter on the geoboard and transition these figures to grid paper.

Differentiation for Remediation: Some students may struggle visually in transferring their learning from the manipulative to the abstract (rubber bands to grid paper.) Additional practice will be necessary.

Differentiation for English Language Learners: Vocabulary activities focusing on the language of perimeter, around, distance, length, and border.

Differentiation for Enrichment: Some students may benefit from building and creating complex figures on the boards or transition directly to grid paper.


Some students will struggle with the abstractness of the grid paper and not be able to “see” the perimeter without building it using manipulatives.


Steps:

1. Pass out Let’s Prove Perimeter worksheet. Ask students to speculate about how they might determine the perimeter of the first figure.

Collect responses. Tell students they will be proving what the perimeter is for a shape. Pass out straw pieces and ask students to again guess as to how these pieces of straw might help us prove the perimeter. Allow students to share ideas with partners and then try to determine the perimeter.

Let students discuss. Circulate. Allow students to share their proof. If necessary, continue with several examples on worksheet.




2. Gather closing thoughts/ideas. Possible topics for Anchor Chart: Proving perimeter of any figure on dot paper can be

accomplished by placing manipulatives within the space between the dots.

Proving perimeter of any figure on dot paper can be accomplished by counting. (20-25 minutes)


3. Transition from dot paper to using geoboards.Remind students of rules for using geoboards.

Keep geoboards on desk. Rubber bands are to be used only on the board itself. Rubber bands have limits to how far they can expand. Careful placement of rubber bands on pegs.

Have students note the similarity between dot paper and geoboards as you pass out geoboards.

Taking straw pieces or toothpicks (whichever fits better into geoboard spaces) model how to show a figure with a perimeter of 10. Lay the straws or toothpicks down in the spaces BEFORE students put the rubber bands on the geoboard.

Give students another perimeter to model: 14. Rather than having students “hold up” their geoboards, you may allow them to do a Gallery Walk and go around the room to look at other students’ figures. (Or use a document camera for students to share.) Continue with several other examples. (15-20 minutes)4. After some time practicing, change the parameters of the Gallery

Walk. As students visit other students’ geoboards, direct them to write the perimeter of the shape on Post-It notes and leave them behind for other students to check.

Discuss misconceptions and errors students are making.

If necessary, allow some students to prove their solutions using manipulatives. (15-20 minutes)5. Pass out Perimeter Practice on Geoboards sheet for students to

solve for perimeter.

If needed, pull some groups of students who are having difficulty to assist one-on-one.

(10 minutes) 6. Administer Perimeter with Geoboards Assessment

(20 minutes)

Segment 4




60-80 minutes

Lesson Format: Whole Group Small Group (Partners) Independent


Resources: Colored straws or pipe cleaners in

three colors. Colored pencils Empty Number Line Grid paper with shapes Finding Perimeter of Polygons with

All Sides GivenFocus:

Find the perimeter of polygons when all side lengths are given.


Math Practice Look For(s):MP5 Use appropriate tools strategically. Students will use physical objects to model perimeter on the geoboard and transition these figures to grid paper.

Differentiation for Remediation: Have students place base-ten blocks above the number line to help calculate the value of each arrow jump.

Differentiation for English Language Learners:Have students write the word side next to each side of one of the rectangles drawn in their notebooks. As the students trace over each of the four sides with a pencil, have them say: Side plus side plus side plus side is the distance around the rectangle. It is the perimeter.

Differentiation for Enrichment: Have students calculate the perimeter of one of the

rectangles if it were to double or triple in size. Students sketch these complex polygons and assign

2-digit numbers to each side. Have students show how they used the number line to help them calculate the perimeter of the complex polygons.


Some students will struggle with the abstractness of the grid paper and not be able to “see” the perimeter without building it using manipulatives.




Steps:

1. Working with a partner, students build the perimeter of as many squares and rectangles as possible.

Each pair of students are given a baggy of eight 3 inch yellow straw segments; eight 4 inch green yellow straw segments; and eight 5 inch pink straw segments .(If Pipe cleaners are substituted for straws, remind students not to bend them since polygons have straight sides.)


Possible polygons: Squares: 3” x 3”(4 yellow ); 4” X 4”(4 green); 5” X 5” (4 pink)Rectangles: 3” X 4” (2 yellow and 2 green), 3” x 5”( 2 yellow and 2 pink), 4” X 5”(2 green and 2 pink)

Using coordinating colored pencils, each student draws the polygons made in their math notebooks.

Tell students the length of each type of pipe cleaner. Yellow pipe cleaners are3 inches long Green pipe cleaners are 4 inches long Pink pipe cleaners are 5 inches long

Students then label each of the polygons’ sides drawn in their notebooks. Remind students to include the unit of inches.

2. Guide students through the process for determining the perimeter of each of their figures. Add process to Anchor Chart:

To find perimeter, we would add up the numbers next to each of the sides to find the total number of inches; Perimeter = side + side+ side+ side+. . .

3. Draw a number line. Model how to calculate the addition of the sides of a figure to find the perimeter of one of the polygons.

Example: For a rectangle with the side lengths of 3”, 3”, 4”, and 4” add the two sides of 3 inches and 3 inches and one of the 4 inch sides together and jump 10 on the number line. Then jump another 4 inches. The perimeter of this rectangle is 14 inches; P= 14 inches.

+ 4

0 10 14

Repeat with other examples as necessary.

4. Have students find the perimeter for the other polygons using Teacher Notes/Reflections:



a number line to model the calculation of the perimeter. Remind students to include inches as the unit.

5. Have students find the perimeter of the shapes on the grid paper using a number line to help calculate the perimeter.

6. Allow students to work on worksheet, Finding Perimeter of Polygons with All Sides Given



Segment 5


80-120 minutes (2 Days)



Resources:

Empty number line Perimeter Practice with Missing

Sides Finding Missing Sides with Tiles Perimeter Practice with Missing

Sides #1

Focus:

Find the perimeter of polygons with one missing side when reasoning about shape attributes.



MP1: Make sense of problems and persevere in solving them. Students will make sense of the problems by interpreting the visual models and determining the value of the missing side.

Differentiation for Remediation:

Students may need to lay construction paper rectangles on top of one another to see the relationship between the sides more clearly.

Differentiation for English Language Learners:

Students may need more experiences with the concept of same.

Differentiation for Enrichment:

Students draw complex polygons with corners and assign 2-digit numbers to all but one of the sides. Students explain in writing how they would find the length of the missing side. Students then calculate the perimeter using a number line.

Potential Pitfall(s): Independent Practice (Homework):

Steps:

1. Draw an outline of a square on the board. Write a 2-digit number next to one of the sides. Write that same 2-digit number next to two more of the sides leaving one side missing its measurement. Ask students what they would need in order to calculate the perimeter. Revisit properties of a square – all sides are equal – so missing measurement would be . . . Model how to calculate the perimeter using a number line.


2. Repeat Step 1 for a rectangle. Students should be able to determine the missing side knowing the attributes of a rectangle. Have a student volunteer come up to the board to calculate the perimeter and model on a number line.



3. Draw an equilateral triangle on the board. Remind students that all three sides of this triangle are the same length. Write a 2-digit number next to two of the sides. Have a student volunteer come up to the board to calculate the perimeter and model it using a number line.


4. Draw two rectangles on the board

A B

3

10 10 3 3

Ask students to Turn & Talk with a partner to figure out the length of the missing sides and determine the perimeter.

5. Make an L shape out of these two rectangles. Write the lengths of all the sides except for one.

3

A 7 s

10

3

10

B

6. If the short side of Rectangle A is 3 units and the length of the long side of Rectangle B is 10 than the missing side is the difference of 10 minus 3 or 7. Model using a number line to find the missing addend.

- 3

0 7 10

7. Substitute the length of the sides of Rectangles A and B with 2-digit numbers. Have students use the number line to calculate the missing side.

To give students additional practice in finding the missing side, use the same 2-digit numbers, but choose a different side to be the missing side.

8. Have students work collaboratively in partners on the Perimeter

10



Practice with Missing Sides



Segment 6


Day 2



Resources: Centimeter grid paper Empty number line Finding Missing Sides of Polygons

Given Perimeter Perimeter Practice with Missing

Sides #2

Focus:

Find the unknown side length of polygons, when the perimeter is given.


Math Practice Look For(s):MP4 Model with mathematics. Students interpret the visual models and equations to compute the missing side lengths.

* Elementary students might use geometric figures, pictures or physical objects and/or a number line to help them interpret the addition or subtraction situation.

MP5 Use appropriate tools strategically. Students use the diagrams to find the missing sider lengths.

* The tools that elementary students might use include: geometric shapes, sketches, and number lines.

Differentiation for Remediation:

Limit the number of sides to 5.

Differentiation for English Language Learners:

To simulate the meaning of the arrows, have students jump forward on a number line taped to the floor when adding. Then when subtracting have students jump backward on a number line taped to the floor.

Differentiation for Enrichment:

Have students roll the dice and create the largest 2-digit number possible for the sides of the polygon.

Potential Pitfall(s): Independent Practice (Homework):

Steps:Option: The following activity can be done on a SmartBoard or can be shared on document camera.

1. On centimeter grid paper draw the outline of a multi-sided polygon with square corners. Record measurements to all sides but one. Label the unknown side with the letter s.




2. Model using a number line add the values for the known sides. Let students share their various methods for adding the known sides.

+10 +14 +5

0 100 110 124 129

The total of the known sides equals 129 cm.


2.2

3. Write P = 164 cm below the shape. On a second number line subtract the total of the known sides from the perimeter (starting at 164 cm) to determine the value of the unknown side.

-5 -20 -4 -100

0 35 40 60 64 164

Write the equation 164 – 129 = sThis does not have to be the manner in which students solve for the unknown so allow students to share their strategies for determining the missing side length.

The value of the remaining side is 35 or s = 35 cm

4. Have students draw a multi-sided polygon with square corners on centimeter paper. Remind students that polygons have straight sides. Limit the number of sides they can draw to no more than eight sides. Have students repeat above steps.



Segment 7

Approximate Time Frame:90-110 minutes



Resources: Paper/pencil Centimeter and inch ruler Student textbook Rectangular objects in classroom Measuring Perimeter Using

Measurement Tools Solving Perimeter Problems -

Summative

Focus:

Finding the perimeter of a polygon using measurement tools with real-life objects.


Math Practice Look For(s):.MP2 Reason abstractly and quantitatively. Students will use quantitative reasoning that entails creating a coherent representation of the object to be measured.

MP4 Model with mathematics. Students will apply the measurement concepts they know to measure objects in everyday life.

MP5 Use appropriate tools strategically.Students will use centimeter and inch rulers to measure various objects within the classroom setting and use number lines to calculate the perimeters of these objects.

MP 6 Attend to precision. Students will label unknown side lengths and calculate accurately using a number line.

Differentiation for Remediation: For those students who have difficulty using a blank number line, give beginning interval markings to start the students off and guide them for the first few side lengths. After the first few intervals have been given, allow the students to continue on by themselves. Also, if students have difficulty remembering which side of the ruler to use, place a thin color-coded sticker on the inch side. Students will then associate inches with the color sticker and use the other side of the ruler when asked to measure units other than inches.

Differentiation for English Language Learners: Directions for each problem should be translated into the student’s predominant language so accuracy can be achieved when solving the problems.

Differentiation for Enrichment: As an extended activity, the enrichment students can look at an object and predict in both centimeter and inch units what the perimeter will measure. They can work with partners and each person can pick an object that their partner will measure. Both the prediction and actual measurement will be recorded for three objects on paper. The difference in both measurements will be noted. The three differences will be added together. The partner with the fewest cm/in difference total will be the winner.

Potential Pitfall(s): If students cannot measure fluently with both centimeter and inch units, practice with rulers should precede the assessment.

Independent Practice (Homework): Students can practice measuring real-life objects at home with a cm/in ruler. Measuring objects using both centimeters and inches should be practiced so the students learn if their answers are reasonable or not.

Steps: Teacher Notes/Reflections:



1. The teacher will review both the centimeter and inch markings on the students’ rulers. The teacher should reiterate that to accurately measure an object, rulers should be analyzed to see if the ruler has a leading edge. If it does, the students should be sure to line the edge up with the “0” marking. A quick check of each student’s ruler should prevent problems during the lesson.

0

2. After the students are comfortable identifying the inch side of the ruler, choose any rectangular object from the classroom, like the top (face) of a tissue box. Have a student draw the rectangle on the board. The teacher will then demonstrate how to use the ruler to measure one of the longer sides of the tissue box. At the time the teacher is measuring the real-life object, a careful demonstration of measuring to the nearest unit should be discussed.

Show the students when measuring the side length that if the ruler does not measure perfectly to the end, analyze the ruler markings to see if the end of the side length is closer to the lower or higher number. If it is halfway or more, the side length should be rounded to the higher number.

The student will record the length in inches on one of the longer sides of the rectangle drawn on the board. Then measure one of the shorter sides of the rectangle. Have the student record this length on the rectangle drawn on the board. Continue and measure and record the remaining two sides.

3. Have students add the side lengths together to find the perimeter. Model calculating the perimeter using a number line with no markings. Explain the beginning of the number line can be marked with a “0”.Example with lengths of 10, 4, 10, and 4.

0 10 14 24 28

4. Steps 2 and 3 should be repeated using the centimeter side of the ruler.

5. When completing the Measuring Perimeter Using Measurement Tools assessment sheet, begin by discussing the pizza question.


+44

+44

+104



Since students will not actually have a slice of pizza in front of them, it will be a great lesson to predict how long the side lengths of a triangular or square slice of pizza might be. Have the students sketch it, write in projected centimeter lengths for all side lengths and calculate the total perimeter using the number line. The students can then sketch a true-to-life size slice of pizza on the back of the paper and measure all the side lengths to the nearest centimeter.

Review: When measuring the side length, if the ruler does not measure perfectly to the end, analyze the ruler markings to see if the end of the side length is closer to the lower or higher number. If it is halfway or more, the side length should be rounded to the higher number.

Then, they can draw their own number line and calculate the total perimeter of the shape. When they have calculated both perimeters, they can compare the predicted and actual measurements and analyze the difference in the perimeters. 6. Students should then find a textbook of their choice. Before they

measure, the students should sketch the top face of the book. After they measure each side length to the nearest inch, the results should be recorded on their sketch. When all side lengths have been recorded to the nearest inch, the perimeter should be calculated using the number line.

7. Before completing the last two problems, explain to the students that the objects they find within the classroom must have a total perimeter of less than 100 cm. Have the students analyze the centimeter unit, find an object they think will fit the parameters of the problem, sketch it and record the side lengths. When they calculate the perimeter on the number line, if the students’ objects have a perimeter over 100 cm, they must look for another object to measure until the object they choose follows the perimeter limits. When they find an appropriate object, they will then sketch it, measure it to the nearest inch and calculate the perimeter on the number line.



8. When the item in Step 7 has been measured using both units, the students can turn to a partner and discuss the question posed asking why there are different perimeters if they measured the same object twice.

9. After all the activities have been completed, have the students form small groups and discuss the following questions:

What strategy did you use to choose an object that had a perimeter of less than 100 cm?

If you made an error in your first choice, how did you adjust your strategy to choose a new object?

What object in the classroom would you predict would have a perimeter of less than 200 cm? Why would you choose that object?


10. Administer Solving Perimeter Problems Summative

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