Question

Sam 在 $90$ 分钟内开了 $96$ 英里。前 $30$ 分钟他的平均速度是每小时 $60$ 英里，第二个 $30$ 分钟的平均速度是每小时 $65$ 英里。最后 $30$ 分钟他的平均速度是每小时多少英里？

Sam drove $96$ miles in $90$ minutes. His average speed during the first $30$ minutes was $60$ mph (miles per hour), and his average speed during the second $30$ minutes was $65$ mph. What was his average speed, in mph, during the last $30$ minutes?

$64$

$65$

$66$

$67$

$68$

答案：D

知识点：路程、速度与时间

难度评级：980

解答：

每段都是半小时。第一段行驶 $60 \cdot \tfrac12 = 30$ 英里，第二段行驶 $65 \cdot \tfrac12 = 32.5$ 英里。前两段共 $62.5$ 英里，还剩 $96 - 62.5 = 33.5$ 英里。最后半小时的速度为 $33.5 / \tfrac12 = 67$ 英里每小时。因此正确答案是 D。

Each leg is half an hour. In the first, Sam drove $60 \cdot \tfrac12 = 30$ miles; in the second, $65 \cdot \tfrac12 = 32.5$ miles. That's $62.5$ miles so far. That leaves $96 - 62.5 = 33.5$ miles for the last half hour, which is a speed of $33.5 / \tfrac12 = 67$ mph. Therefore, the answer is D.

2018 AMC 10B 第 2 题

答案：D

难度评级：980

解答：

其他年份的第 2 题