1985 AMC 8 Problem 19

Attempt Problem 19 of the 1985 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1985 AMC 8 solutions, or check the answer key.

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19.

If the length and width of a rectangle are each increased by 10%,10\%, then the perimeter of the rectangle is increased by

1%1\%

10%10\%

20%20\%

21%21\%

40%40\%

Answer: B
Concepts:percentageperimeter

Difficulty rating: 800

Solution:

The new perimeter is 2(1.1+1.1w)=1.12(+w),2(1.1\ell + 1.1w) = 1.1 \cdot 2(\ell + w), which is 1.11.1 times the old perimeter.

That is a 10%10\% increase.

Thus, the correct answer is B .

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