2010 AMC 8 第 13 题

先试着解答 2010 AMC 8 第 13 题,然后核对你的答案与精心整理的解答,解答来自 LIVE by Po-Shen Loh。你也可以参加完整限时模拟考试、查看全部 2010 AMC 8 解答,或核对答案。

所有题目均经美国数学协会(MAA)官方合法授权使用。

13.

一个三角形的三边长度(单位为英寸)是三个连续整数。最短边长度是周长的 30%30\%。最长边长度是多少?
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
答案:E
知识点:周长一次方程百分数
小提示:
使用最短边为周长 30%30\% 这个条件
Use the condition that the shortest side is 30%30\% of the perimeter.
大提示:
设三条边长是从最短边开始的三个连续整数
Let the side lengths be three consecutive integers starting with the shortest.
解答:
设最短边长为 ss。三边长度为 ss、s+1s+1、s+2s+2,周长为 3s+33s+3。因为 s=0.3(3s+3)s = 0.3(3s+3),所以 s=0.9s+0.9s = 0.9s + 0.9 。因此 0.1s=0.90.1s = 0.9,得到 s=9s = 9,最长边为 s+2=11s + 2 = 11。
所以正确答案是 E。
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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