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 GLE 0706.2.4.

342 Percent

Proportions and Equations

PART A BCD

Problem-Solving Investigation

Main Idea

Multi-Part

Lesson 2

Main Idea Solve problems by determining reasonable answers.

Understand Doug and his dad spent $28. Doug thinks that $5 is about 15% of the bill.

Plan Make a bar diagram to represent 100%.

Solve Divide it into ten parts, each representing 10%.

$2.80 $2.80 $2.80 $2.80 $2.80 $2.80 $2.80 $2.80 $2.80 $2.80

$28

So, a 10% tip would be $2.80.

If 10% = $2.80, 5% is $2.80 ÷ 2 or $1.40.

So, a 15% tip would be $2.80 + $1.40 or $4.20. A $5 tip is reasonable.

Check $28 × 0.15 = $4.20. So, $5 is a reasonable estimate.

1. Explain how to use mental math to find 15% of a number.


2. E WRITE MATH Write two real-world problems involving tips. One should
   have a reasonable answer and the other should not have a reasonable
   answer.

Problem-Solving Investigation

Main Idea

Determine Reasonable Answers

DOUG: My dad and I are at a restaurant. Our

bill is $28. We want to leave a tip that is

15% of the bill. I think he should leave $5

for the tip.

YOUR MISSION: Determine whether it is reasonable

for Doug’s dad to leave $5 as the tip.

342_343_C06_PSI_895130.indd 342 12/30/09 4:06 PM