2010 AMC 8 Problem 13

Attempt Problem 13 of the 2010 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 2010 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

13.

The lengths of the sides of a triangle in inches are three consecutive integers. The length of the shortest side is 30%30\% of the perimeter. What is the length of the longest side?
 7 \ 7
 8 \ 8
 9 \ 9
 10 \ 10
 11 \ 11
Answer: E
Concepts:perimeterlinear equationpercentage
Small hint:
Use the condition that the shortest side is 30%30\% of the perimeter.
Big hint:
Let the side lengths be three consecutive integers starting with the shortest.
Solution:
Let ss be the smallest length. Then, all the side lengths are s,s, s+1,s+1, s+2.s+2. This would make the perimeter equal to 3s+3.3s+3. Since s=0.3(3s+3),s = 0.3(3s+3), then s=0.9s+0.9.s = 0.9s + 0.9 . This makes 0.1s=0.9,0.1s = 0.9, so s=9s = 9 which makes the longest side length s+2=11.s + 2 = 11.
Thus, the answer is E .
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