Question

如果不下雨，Shelby 骑滑板车的速度是每小时 $30$ 英里；如果下雨，速度是每小时 $20$ 英里。今天她早上在晴天中骑行，晚上在雨中骑行，总共 $40$ 分钟骑了 $16$ 英里。她在雨中骑了多少分钟？

Shelby drives her scooter at a speed of $30$ miles per hour if it is not raining, and $20$ miles per hour if it is raining. Today she drove in the sun in the morning and in the rain in the evening, for a total of $16$ miles in $40$ minutes. How many minutes did she drive in the rain?

$18$

$21$

$24$

$27$

$30$

答案：C

知识点：路程、速度与时间一次方程

难度评级：1240

解答：

设 $t$ 为雨中骑行的分钟数。她在雨中骑了 $20\cdot\frac{t}{60}$ 英里，在晴天中骑了 $30\cdot\frac{40-t}{60}$ 英里。

令总距离为 $16$ ，得到所以 $1200-10t=960$ ， $t=24$ 。 $\frac{20t+30(40-t)}{60}=16,$

因此，正确答案是 C。

Let $t$ be the number of minutes driven in the rain. She covers $20\cdot\frac{t}{60}$ miles in the rain and $30\cdot\frac{40-t}{60}$ miles in the sun.

Setting the total to $16$ gives $\frac{20t+30(40-t)}{60}=16,$ so $1200-10t=960$ and $t=24.$

Thus, the correct answer is C.

2010 AMC 12B 第 7 题

答案：C

难度评级：1240

解答：

其他年份的第 7 题