14.5 Represent Subtraction of Fractions

14.5 Represent Subtraction of Fractions

I can write equations and find the difference of fractions with like denominators.

Multiple Select

Launch: Which of the following sums are equal to 22/17?

• 5/17+4/17+3/17+10/17

• 3/17+8/17+3/17+10/17

• 6/17+4/17+3/17+5/17+2/17+2/17

• 12/17+10/17

• 11/7+11/7+9/17+3/17

Spark Your Learning

Marcy and Lindsey are playing games at a local carnival. They play the game “Measure Your Strength,” and their results are shown. 

Find how much farther Marcy hits the puck up the board than Lindsey does.

Multiple Choice

Marcy hits the puck ____ farther up the board than Lindsey does.

• 6/8​​

• 4/8​​

• 2/8​​

Marcy hits the puck 2/8 farther up teh board than Lindsey.

When you compare 6/8​​ and 4/8​​, the difference is 2/8​​.

Build Understanding

Leo checked the levels of grape drink in this cooler before and after lunch. How much grape drink was used during lunch? The cooler holds 1 gallon.

Multiple Choice

How is the starting amount of grape drink represented on the sample fraction model?

• Three of 10 parts are shaded.

• Six of 10 parts are shaded.

• Nine of 10 parts are shaded.

It's 9/10 full.

The starting amount is 9/10​​ gallon, so 9 of 10 parts are shaded on the sample fraction model.

Multiple Choice

Which fraction model shows a circled section representing the solution to the problem?

• The first image

• The second image

• The third image

It's the second image.

Before lunch, there was 9/10​​ gallon of grape drink in the cooler. So 9 one-tenth parts of the fraction model are shaded. After lunch, 3/10​​ gallon of grape drink is left in the cooler. To show this, shaded tenths are crossed off until only three shaded tenths remain. The number of crossed-off tenths represents the amount of drink that was used during lunch.

Multiple Choice

Which equation models the problem?

• 9/10 - 6/10 = 3/10

• 10/10 - 1/10 = 9/10

• 9/10 + 3/10 = 12/10

It's 9/10 - 3/10 = 6/10

At the start of lunch, there was 9/10​​ gallon of grape drink. This is represented by shading 9 tenths sections on the visual fraction model. At the end of lunch, 3/10​​ gallon of grape drink was left in the cooler. This is represented by crossing off 6 of the 9 shaded tenths. The equation that models this problem is 9/10​−6/10​=3/10​​.

Step it Out

Ross makes popcorn at a carnival. At the start of his shift, the container of kernels weighs 11/12​ ​pound. During his shift, he uses 3/12​

​pound of the kernels. How many pounds of kernels are left after Ross’s shift?

Multiple Choice

Select the equation that models the situation. The weight of kernels left after Ross's shift is represented by p.

• p = 12/12 ​− 11/12​

• p = 11/12 ​− 3/12​

• p = 8/12 ​− 3/12​

We would use

p = 11/12 − 3/12​

​

Ross starts with 11/12​ pound of kernels. He uses 3/12​​ pound of kernels during his shift. Subtract the weight of kernels used from the weight of kernels at the start to find how many pounds of kernels are left after Ross's shift.

p = 11/12 ​− 3/12​