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Speed problem

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Speed problem

by sukhman » Sun Mar 13, 2016 4:08 am
If cars F and S are racing on same circular race track and each is travelling at a constant rate for 20 laps around the track , what is the ratio of F's rate to S's rate ?
1) During F's first 18 laps around the track , F passes S 3 times
2) F is travelling 3 miles per hour faster than S
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Source: — Data Sufficiency |
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by MartyMurray » Sun Mar 13, 2016 8:49 pm
Statement 1:

This might seem to provide enough information for determining the answer, but the truth is that we don't know during which laps F passed S. F could have passed S during laps 5, 10 and 15 or during laps 6, 12, and 18, and either way at the end of 18 laps F would have passed S three times during F's first 18 laps.

Also, F could have passed S at the beginning or end of any lap.

In any case, we cannot from this tell the ratio of their speeds.

Insufficient.

Statement 2:

The difference between their speeds is not sufficient for determining the ratio of their speeds. Here are some examples.

F - 5 S - 2 Ratio - 5:2

F - 6 S - 3 Ratio - 2:1

Statements Combined:

In combining the statements we still don't have enough information to pin down in which laps F passed S or the speeds of the two cars.

Insufficient.

The correct answer is E.
Marty Murray
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