5-26th grade math

Adding and Subtracting with Like Denominators

Objectives

• Add and subtract fractions and mixed numbers with like denominators.

• Why? To know how to solve all types of number sense problems.

California State Standards

• NS 2.1: Solve problems involving addition, subtraction, … of positive fractions and explain why a particular operation was used for a given situation…

• NS 2.0 : Calculate and solve problems involving addition, subtraction, …

• MR 2.1: Use estimation to verify the reasonableness of calculated results.

Vocabulary

• Like denominators-– fractions whose denominators are the same• +

• Simplify (simplest form, reduced form)-– when the GCF of the numerator and denominator

is one• 2 = (divide by 5) = 1 10 = (divide by 5) 5

How to Add Fractions with like Denominators

Example 1. + 1. Add the numerator.2. Keep the denominators

the same.3. Simplify, if possible.

Here’s how to solve: + =

4 = 8

12

How to Add Fractions with like Denominators, with a “Mixed/Improper” Answers.

Example 2.9 3 + 7 7 8 81. Add the fractions.2. Add the whole numbers.3. Simplify the sum.

9 3 87 7+ 8

= 10 8

=16 10 8 10/8 = 1 2/10 = 1 + 16 == 16

How to Subtract Fractions with like Denominators

Example 37 - 310 101. Subtract the numerators2. Use the common

denominator.3. Simplify, if possible.

7 - 310 10

4 = 210 5

How to Subtract Fractions with like Denominators, when needing “to borrow.”

4 - 2

1. Rename the top fraction before you subtract, because <.

2. Subtract the fractions and then whole numbers.

3. Simplify, if possible.

4 - 2

3 4 4- 2 3- 4 2 = 1 4 2= 1= 1

Try It!1) 11 - 4 15 15

2) +

3) -

4) 7 - 3 12 12

5) 8 - 2 9 9

Answers:1) 7 15

2)

3)

4) 5)

How it works ….

2) 1/8 + 3/8 = 4/8 = ½

3) 7/8- 5/8 = 2/8 = ¼

4) 7/12 – 3/12 = 4/12 = 1/3

5) 8/9 – 2/9 = 6/9 = 2/3

Try some more!!

6) 4 - 2

7) 8 6 + 4 7 8 8

8) 3 6 + 1 5 7 7

9) 6 – 4

Answers:6) 1

7) 13 5 8

8) 5 4 7

9) 1

How it works!6) 4 1/3 – 2 2/3 = 3 3/ 3 – 2 2/3 1 1/3

7) 8 6/8 + 4 7/8 = 13/8 = 1 5/88 + 4 = 1212 + 1 5/8 = 13 5/8

8) 3 6/7 + 1 5/7 11/7 = 1 4/73 + 1 = 44 + 1 4/7 = 5 4/7

9) S6 - 4 ¾ 5 4/4 - 4 ¾ = 1 ¼

Objective Review

• Add and subtract fractions and mixed numbers with like denominators.

Why? You know how to solve all types of number sense problems.

Independent Practice

1. Complete problems 13-19.

2. Problems 20, 21 for a challenge.

3. Remember to copy the problem first.

4. Show all of your work!

• When finished:– If time, complete the

Mixed Review problems 22-24.

– If still more time, complete your Accelerated Math.