# Error analysis describe and correct the error in

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Chapter 7 / Exercise 122
Mathematical Practices, Mathematics for Teachers: Activities, Models, and Real-Life Examples
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21. ERROR ANALYSISDescribe and correct theerror in using the percent of change to find 25 is decreased by 40%.
25
22. VIDEO GAMELast week, you finished Level 2 of a video game in 32 minutes. Today, you finish Level 2 in 28 minutes. What is your percent of change?
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Chapter 7 / Exercise 122
Mathematical Practices, Mathematics for Teachers: Activities, Models, and Real-Life Examples
Larson Expert Verified
Section 12.2Percents of Increase and Decrease 65Write and solve an equation to answer the question.34. What number is 25% of 64? 35. 39.2 is what percent of 112?36. 5 is 5% of what number? 37. 18 is 32% of what number?38. MULTIPLE CHOICEWhich equation shows direct variation? Ayx=1 Byx=10 Cy=4xDxy=Find the percent of change in the area.30. RUNNINGFind the percent of change in the time to run a mile from June to September.31. CRITICAL THINKINGA number increases by 10% and then decreases by 10%. Will the result be greater thanless than, or equaltothe original number? Explain.32. DONATIONSDonations to an annual fundraiser are 15% greater this year than last year. Last year, donations were 10% greater than the year before. The amount raised this year is \$10,120. How much was raised 2 years ago?33. Forty students are in the science club. Of those, 45% are girls. This percent increases to 56% after new girls join the club. How many new girls join?10 ftJuneSeptember5Identify the percent of change as an increaseor decrease. Then find the percent of change. Round to the nearest tenth of a percent, if necessary.23. 14to 1224. 45to 3525. 38to 7826. 54to 3827. CRITICAL THINKINGExplain why a change from 20 to 40 is a 100% increase, but a change from 40 to 20 is a 50% decrease.28. POPULATIONThe table shows population data YearPopulation2000118,0002006138,000for a community. a. What is the percent of change from 2000 to 2006?b. Use this percent of change to predict the population in 2012.29. GEOMETRYSuppose the length and width of the sandbox are doubled.a. Find the percent of change in the perimeter.b. Find the percent of change in the area.30. RUNNINGFind the percent of change in the time to run a mile from June to September.31. CRITICAL THINKINGA number increases by 10% and then decreases by 10%. Will the result be greater thanless than, or equaltothe original number? Explain.32. DONATIONSDonations to an annual fundraiser are 15% greater this year than last year. Last year, donations were 10% greater than the year before. The amount raised this year is \$10,120. How much was raised 2 years ago?33. Forty students are in the science club. Of those, 45% are girls. This percent increases to 56% after new girls join the club. How many new girls join?10 ftJuneSeptember, 6 ft
66Chapter 12Percents12Study HelpMake a summary triangle to help you study these topics.1. finding the percent given a number and a part of the number2. finding the number given a part of the number and a percent3. percent of increase4. percent of decreaseAfter you complete this chapter, make summary triangles for the following topics.5. discount6. markup7. simple interestYou can use a summary triangleto explain a concept. Here is an example of a summary triangle for finding a percent of a number.Multiply the percent(in decimal or fraction form)by the number.Findinga percentof a numbera= pwExample: What number is 25% of 80?a= 80 = 20 25100“I hope my owner sees my summary triangle. I just can’t seem to learn ‘roll over’.”
Write and solve an equation to answer the question.
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