Question

去年夏天，Town Lake 上生活的鸟中 $30\%$ 是鹅， $25\%$ 是天鹅， $10\%$ 是鹭， $35\%$ 是鸭。在不是天鹅的鸟中，鹅占百分之几？

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?

$20$

$30$

$40$

$50$

$60$

答案：C

知识点：百分数条件概率

难度评级：990

解答：

不是天鹅的鸟占总数的 $100\% - 25\% = 75\%$ ，而鹅占总数的 $30\%$ 。所求比例为 $\dfrac{30}{75} = \dfrac{2}{5} = 40\%.$

因此，正确答案是 C。

The birds that are not swans make up $100\% - 25\% = 75\%$ of the total, and geese are $30\%$ of the total. The requested fraction is $\dfrac{30}{75} = \dfrac{2}{5} = 40\%.$

Thus, the correct answer is C.

2011 AMC 12A 第 5 题

答案：C

难度评级：990

解答：

其他年份的第 5 题