7th Grade Math

GLE 0706.1.2 Apply and adapt a variety of appropriate strategies to problem solving, including estimation,

and reasonableness of the solution. Also addresses SPI 0706.2.3.

Problem-Solving Investigation

202 Equations and Inequalities

Addition and Subtraction Equations

PART A BCD

Main Idea Solve problems using the work backward strategy.

Work Backward

MIGUEL: Yesterday, I earned extra money by

doing yard work for my neighbor. Then I spent

$5.50 at the convenience store and four times

that amount at the bookstore. Now I have

$7.75 left.

YOUR MISSION: Work backward to find how

much money Miguel had before he went to the

convenience store and the bookstore.

Understand You know he has $7.75 left. You need to find the amount he started with.

Plan Start with the end result and work backward.

Solve He has $7.75 left.

Undo the four times $5.50 spent at the bookstore.

Since $5.50 × 4 is $22, add $7.75 and $22.

Undo the $5.50 spent at the convenience store.

Add $5.50 and $29.75.

So, Miguel had $35.25 to start with.

$7.75

+ $22.00

$29.75

+ $5.50

$35.25

Check Assume Miguel started with $35.25. He spent $5.50 and $22. He had

$35 - $5.50 - $22 or $7.75 left. So, $35.25 is correct. ✓

1. Explain when you would use the work backward strategy to solve a problem.


2. Describe how to solve a problem by working backward.


3. E Write Math Write a problem that could be solved by working backward.
   Then write the steps you would take to find the solution to your problem.

Multi-Part

Lesson 1

202_203_C04PSI_895130.indd 202 1/4/10 10:28 AM