AMC 8 2012 Problem 9
AMC8 2012 年第 9 题
方程与不等式★★☆☆☆
The Fort Worth Zoo has a number of two-legged birds and a number of four-legged mammals. On one visit to the zoo, Margie counted 200 heads and 522 legs. How many of the animals that Margie counted were two-legged birds?
Fort Worth 动物园有一些两只腿的鸟，和一些 4 只腿的哺乳动物。一次 Margie 去动物园，数到了 200 个头，522 条腿。那么 Margie 数到的动物中，有多少是两只腿的鸟？
- A.
- B.
- C.
- D.
- E.
正确答案 · Correct Answer
C
解析 · Solution
Solution 1
All 200 200 heads belonged to animals with at least two legs, accounting for 400 400 of the 522 522 legs. The additional 122 122 legs belonged to four-legged mammals, each of which had two additional legs. So Margie saw 122 2 = 61 2 122 =61 fourlegged mammals and 200 − 61 = 139 200−61=139 birds. Answer: 𝐶 C .
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