lesson 18: i can use basic facts to estimate quotients with two-digit divisors. 5th grade module 2...

5th Grade Module 2 – Lesson 18

Lesson 18: I can use basic facts to estimate quotients with two-

digit divisors.


Divide By Multiples of 10

12,000 ÷ 40

12,000 ÷ 10 ÷ 4

1,200 ÷ 4

300



12,000 ÷ 400

12,000 ÷ 100 ÷ 4 120 ÷ 4

30



12,000 ÷ 4,000

12,000 ÷ 1,000 ÷ 4 12 ÷ 4

3



360,000 ÷ 6,000 360,000 ÷ 1,000 ÷ 6 360 ÷ 6

60



490,000 ÷ 700

490,000 ÷ 100 ÷ 7 4,900 ÷ 7

700



640,000 ÷ 80

640,000 ÷ 10 ÷ 8

64,000 ÷ 8

8,000


Estimate and Divide

812 ÷ 39 Say the divisor rounded to the nearest ten…÷ 40

Name the multiple of 40 that’s closest

to 812…800

Estimate the value…

20


Estimate and Divide



to 183…180


6


Estimate and Divide



to 420…420


6


Estimate and Divide


0

Name the multiple of 100 that’s closest to

800…800


8


Estimate and Divide

8,191 ÷ 92 Say the divisor rounded to the nearest ten…÷ 90


to 8,100…8,100


90


Application Problem

Sandra bought 38 DVD movies for $874. Give an

estimate of the cost of each DVD movie.

Solution on next slide…


Solution

$874 ÷ 38 =800 ÷ 40 =

(800 ÷ 10) ÷ 4 =80 ÷ 4 =

$20 per DVD


Concept Development

8,095 ÷ 23

What’s the whole (or dividend) in this problem?

8,095

What’s the divisor? 23

Let’s use rounding to find an estimated quotient!

First, let’s round the divisor to the nearest ten!

23 ≈ 20Let’s record our estimation

below.

8,095 ÷ 23≈ ____ ÷ 20

We need to round our whole, 8095, to a number that can easily be divided

by 20. Turn and share your ideas to your partner.

We can round 8095 to 8000 since I can use

mental math to divide 8000 by 20.

Now let’s solve.Remember to take out the

10 to help you.

80008000 ÷ 10 ÷ 2 800 ÷ 2 400


2,691 ÷ 48

Take out your journal. Let’s estimate the quotient. What do we do first?

1st – Round the Divisor 48 ≈ 50 2,691 ÷ 48≈ ____ ÷ 502nd – Round the Whole (dividend)

Think…When we round for division we want to make sure our dividend is a multiple of the divisor. We

have to think of the nearest multiple of 50.

2700

Let’s solve.Taking out the 10 in 50.

2700 ÷ 10 ÷ 5 270 ÷ 5

2,691 ÷ 48 ≈ 54

= 54

Problem 2


Problem 3

5,484 ÷ 71Work with your partner and solve the estimated quotient.

Remember we are finding the estimated quotient!

1. Round the Divisor2. List the multiples of the

rounded divisor to find the one that is closest to 70

3. Use the closest multiple as your rounded whole number.

4. Divide using the rounded digits.

5. Check to see if your estimated quotient makes sense.

Volunteer to Share Solution:

Solution on next slide…


Solution 5,484 ÷ 71 ≈ 5,600 ÷ 705,600 ÷ 10 ÷ 7 560 ÷ 7 ≈ 80

5,484 ÷ 71 ≈ 80


Work independently to estimate the quotient. Check your work with your partner.

Solution (use ink tools):

9,215 ÷ 95


Get Ready to Complete theProblem Set on Your Own!

Complete Pages 2.E.33 & 2.E.34You will have 15 minutes to work.

Try your Best!


LET’S DEBRIEF• When estimating Problem 1(g), what did you choose for

your unit, 70 or 80? Why? How did it affect the way you estimated the whole?

• Look back at Problem 2 and 4. How was your approach similar in solving? How was it different?

• When solving Problem 3(b), could a mental math approach have been used? (14 apps x $2 – 14 cents) Explain.


EXITTICKETPage 2.E.35

lesson 18: i can use basic facts to estimate quotients with two-digit divisors. 5th grade module 2...

Documents

slide slide

th grade module

dvd slide

nearest multiple

thats closest

dvd movies

mental math

application problem