AMC12 2011 A

AMC12 2011 A · Q5

AMC12 2011 A · Q5. It mainly tests Fractions, Percent.

Last summer $30\%$ of the birds living on Town Lake were geese, $25\%$ were swans, $10\%$ were herons, and $35\%$ were ducks. What percent of the birds that were not swans were geese?

去年夏天，Town Lake上生活的鸟中有$30\%$是鹅，$25\%$是天鹅，$10\%$是鹭，$35\%$是鸭子。不是天鹅的鸟中，有百分之多少是鹅？

(A) 20 20

(B) 30 30

(D) 50 50

(E) 60 60

Answer

Correct choice: (C)

正确答案：（C）

Solution

To simplify the problem, WLOG, let us say that there were a total of $100$ birds. The number of birds that are not swans is $75$. The number of geese is $30$. Therefore the percentage is just $\frac{30}{75} \times 100 = 40 \Rightarrow \boxed{C}$

为简化问题，不妨设一共有$100$只鸟。不是天鹅的鸟有$75$只。鹅有$30$只。因此所求百分比为$\frac{30}{75} \times 100 = 40 \Rightarrow \boxed{C}$。

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