After school, Maya and Naomi headed to the beach, 6 miles away. Maya decided to bike while Naomi took a bus. The graph below shows their journeys, indicating the time and distance traveled. What was the difference, in miles per hour, between Naomi's and Maya's average speeds?

A. 6

B. 12

C. 18

D. 20

E. 24

1. 2020 AMC 8 官方解析

Average speed equals the total distance traveled divided by the elapsed time. Maya covered the distance of 6 miles in 30 minutes, which is $\frac{1}{2}$ of an hour. Her average speed was $6 \div \frac{1}{2} = 12$ miles per hour. Naomi covered the same distance in 10 minutes, which is $\frac{1}{6}$ of an hour. Her average speed was $6 \div \frac{1}{6} = 36$ miles per hour. The difference between their average speeds was $36 - 12 = 24$ miles per hour.

平均速度等于行驶的总距离除以经过的时间 . Maya在 30 分钟内行驶了 6 的英里的距离，这是一个小时的$\frac{1}{2}$ . 她的平均速度为$6 \div \frac{1}{2} = 12$ 英里每小时 . Naomi在10 分钟内行驶了相同的距离，这是一个小时的$\frac{1}{6}$ . 她的平均速度为$6 \div \frac{1}{6} = 36$英里每小时 . 故她们的平均速度之差为 $36 - 12 - 24$ 英里每小时 .