Question

Mary 从家沿上坡路步行 $1$ km 到学校需要 $30$ 分钟，但沿同一路线从学校回家只需 $10$ 分钟。她往返全程的平均速度是多少 km/hr？

It takes Mary $30$ minutes to walk uphill $1$ km from her home to school, but it takes her only $10$ minutes to walk from school to home along the same route. What is her average speed, in km/hr, for the round trip?

$3$

$3.125$

$3.5$

$4$

$4.5$

答案：A

知识点：路程、速度与时间单位换算调和平均数

难度评级：1130

解答：

Mary 总共走 $2$ km，用时 $30+10=40$ 分钟，即 $\dfrac23$ 小时。

平均速度为 $2 \div \dfrac23 = 3$ km/hr。

所以正确答案是 A。

Mary walks a total of $2$ km in $30+10=40$ minutes, which is $\dfrac23$ hour.

Her average speed is $2 \div \dfrac23 = 3$ km/hr.

Thus, the correct answer is A.

2003 AMC 12A 第 4 题

答案：A

难度评级：1130

解答：

其他年份的第 4 题