Question

Mike 骑了 $15$ 圈，用时 $57$ 分钟。假设他全程速度不变，那么他在前 $27$ 分钟大约骑了多少圈？

Mike cycled $15$ laps in $57$ minutes. Assume he cycled at a constant speed throughout. Approximately how many laps did he complete in the first $27$ minutes?

$5$

$7$

$9$

$11$

$13$

答案：B

知识点：比与比例估算

难度评级：560

解答：

设前二十七分钟骑了若干圈，并用未知数表示。

$\dfrac{15}{57} = \dfrac{x}{27}.$

交叉相乘，得到 $x = \dfrac{15}{57} \cdot 27 = \dfrac{135}{19} \approx 7.$

所以正确答案是 B。

We can set up a proportion to solve this problem:

$\dfrac{15}{57} = \dfrac{x}{27}.$

Cross multiplying, we get $x = \dfrac{15}{57} \cdot 27 = \dfrac{135}{19} \approx 7.$

Thus, B is the correct answer.

2022 AMC 10A 第 2 题

答案：B

难度评级：560

解答：

其他年份的第 2 题