Question

一个湖中有 $250$ 条鳟鱼，还有其他多种鱼。一位海洋生物学家从湖中捕捉并放回 $180$ 条鱼作为样本，其中 $30$ 条被识别为鳟鱼。假设样本中鳟鱼占总鱼数的比例与湖中相同，湖中共有多少条鱼？

A lake contains $250$ trout, along with a variety of other fish. When a marine biologist catches and releases a sample of $180$ fish from the lake, $30$ are identified as trout. Assume that the ratio of trout to the total number of fish is the same in both the sample and the lake. How many fish are there in the lake?

$1250$

$1500$

$1750$

$1800$

$2000$

答案：B

知识点：比与比例

难度评级：720

视频讲解：

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文字解答：

样本中鳟鱼比例为 $\dfrac{30}{180} = \dfrac{1}{6}$ 因此湖中所有鱼数是鳟鱼数的 $6$ 倍。

湖中鱼的总数为 $6 \cdot 250 = 1500$ 。

所以正确答案是 B。

Note that $\dfrac{30}{180} = \dfrac{1}{6}.$ This means that a sixth of the fish in the lake are trout, or in other words, the total number of fish is $6$ times the number of trout.

Therefore, there are $6 \cdot 250 = 1500$ fish in the lake.

Thus, B is the correct answer.

2023 AMC 8 第 5 题

答案：B

难度评级：720

视频讲解：

文字解答：

其他年份的第 5 题