Unit 6, Lesson 12
Solving Problems about Percent Increase or Decrease
Grade 7
Practice
A backpack normally costs \$25 but it is on sale for \$21. What percentage is the discount?
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Problem 2
Find each product.
- \(\frac25 \boldcdot (\text-10)\)
- \(\text-8 \boldcdot \left(\frac {\text{-}3}{2}\right)\)
- \(\frac{10}{6} \boldcdot 0.6\)
- \(\left(\frac {\text{-}100}{37}\right) \boldcdot (\text-0.37)\)
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Problem 3
Select all expressions that show \(x\) increased by 35%.
\(1.35x\)
\(\frac{35}{100}x\)
\(x + \frac{35}{100}x\)
\(( 1+0.35)x\)
\(\frac{100+35}{100}x\)
\((100 + 35)x\)
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Problem 4
Complete each sentence with the word discount, deposit, or withdrawal.
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Clare took \$20 out of her bank account. She made a _____.
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Kiran used a coupon when he bought a pair of shoes. He got a _____.
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Priya put \$20 into her bank account. She made a _____.
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Lin paid less than usual for a pack of gum because it was on sale. She got a _____.
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Problem 5
Here are two stories:
- The initial freshman class at a college is 10% smaller than last year’s class. But then during the first week of classes, 20 more students enroll in the class. There are then 830 students in the freshman class.
- A store reduces the price of a computer by \$20. Then during a 10% off sale, a customer pays \$830 for the computer.
Here are two equations:
- \(0.9x+20=830\)
- \(0.9(x-20)=830\)
- Decide which equation represents each story.
- Explain why one equation has parentheses and the other doesn’t.
- Solve each equation, and explain what the solution means in the situation.
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Problem 6
A marimba (muh-RIM-bah) is a musical instrument that came from Africa and is used throughout Central America. A marimba has wooden bars of different lengths. It is played by striking the bars with a mallet.
On one marimba, the longest bar measures \(15\frac38\) inches long. Each bar after that is \(\frac38\) inch shorter than the bar before it. The shortest bar on the marimba is \(7\frac12\) inches long. Write and solve an equation to find the number of bars on this marimba.
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