1956 AMC 12 第 22 题

Question

琼斯第一次旅行走了

50

英里。后来一次旅行中，他以原来三倍的速度走了

300

英里。新旅行时间与原旅行时间相比是：

Jones covered a distance of

50

miles on his first trip. On a later trip he traveled

300

miles while going three times as fast. His new time compared with the old time was:

三倍

three times as much

两倍

twice as much

相同

the same

一半

half as much

三分之一

a third as much

将每次旅行时间写成路程除以速度

Write each travel time as distance divided by speed

若原速度为

v

，比较

\frac{50}{v}

与

\frac{300}{3v}

If the old speed is

v,

compare

\frac{50}{v}

with

\frac{300}{3v}

若第一次的速度为

v

，则原旅行时间为

\frac{50}{v}

。后一次的旅行时间为

\frac{300}{3v}=\frac{100}{v}=2\left(\frac{50}{v}\right)\text{。}

因此，新旅行时间是原来的两倍。

正确答案是 B。

If the first speed was

v,

the old time was

\frac{50}{v}.

The later time was

\frac{300}{3v}=\frac{100}{v}=2\left(\frac{50}{v}\right).

Thus the new time was twice the old time.

The correct answer is B.

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