Tag Archives: percent change

09.09.14
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SAT, Algebra 1 – percent change

Q: Last year, Emmy was 40 inches tall.  This year, she is 42 inches tall.  By what percent has her height increased?

 Answer: 5%

 Explanation:  Percent change is calculated by the following formula:

 (New – Original)/Original  x 100%

 (42 – 40)/40 = 2/40 = .05

 .05 x 100% = 5%

 Since it is positive, this is a percent increase.

My TI-84 Plus program PRCNTCHG will calculate this, too.

 

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09.01.14
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SAT – Percent change

Q: If the length of a rectangle is increased by 30%, while the width is decreased by 10%, by how much will the area increase? Give the answer as a percent.
 
Answer: 17%
Explanation:  Choose the length and width of the original rectangle to be 10.  Then, the length and width of the new rectangle are 13 and 9 (by increasing 30% and decreasing 10%).  The original area is 10 x 10 = 100.  The new area is 13 x 9 = 117.  The percent increase from 100 to 117 is (117-100)/100 = 17/100 = 17%.
Note that if this were an SAT problem with answer choices, you should immediately eliminate any ‘too easy’ answers, such as those related to the numbers 30 and 10 too directly.  Eliminate 20% and 40%.
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