Is the answer wrong? -- Data sufficiency in simple maths

julia27 · 发表于 2015-5-9 22:53:33

Here is the problem:
Two racecar drivers, A and B, are driving around a circular track. If A is 200 meters behind B and both drivers drive their respective constant rates, how long, in second, will it take for A to catch up to B?

The circumference of the racetrack is 1,400 meters.
B is driving 25 meters per minute faster than A.

Given answer is (B)

My questions:
1. B is faster than A, how can A catch up to B? Shouldn't it be B to catch up to A?
2. Then, if B is catching up A on a circular track, the difference between them is not 200 meters, but (the circumference - 200) meters, right? Thus my asnwer is actually (C)!

老李同志 · 发表于 2015-5-10 10:42:09

我晕，题目没有说他们两个的速度谁快谁慢啊。

而且他们是往一个方向走的，所以差距是200m，而不是周长-200m。

列个公式就是 Va·t-Vb·t=200m

所以不需要知道周长，只需要B的条件就可以解出来

julia27 · 发表于 2015-5-10 14:25:36

老李同志发表于 2015-5-10 10:42
我晕，题目没有说他们两个的速度谁快谁慢啊。

而且他们是往一个方向走的，所以差距是200m，而不是周长-20 ...

sorry，（2）里说的B比A快，所以不应是B追A么。。。

Is the answer wrong? -- Data sufficiency in simple maths

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