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Faster way to solve this rates problem?

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Faster way to solve this rates problem? [#permalink] New post 24 Aug 2011, 21:00
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A boat traveled upstream a distance of 90 miles at an average speed of (v-3) miles per hour. It then traveled the same distance downstream at a average speed of (v+3) miles per hour. If the trip upstream took half an hour longer than the trip downstream, how many hours did it take to make the trip downstream?

A. 2.5

B. 2.4

C. 2.3

D. 2.2

E. 2.1

The way I tried to solve this problem was by setting (90)/(v-3) = (90)/(v+3) + 0.5. Then, I can solve for v but that would take a long time. I could also use the answer choices to solve for v, and then test it using the equation but that seems to take just as long. Is there a better way?
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Re: Faster way to solve this rates problem? [#permalink] New post 25 Aug 2011, 05:27
Liquidus wrote:
A boat traveled upstream a distance of 90 miles at an average speed of (v-3) miles per hour. It then traveled the same distance downstream at a average speed of (v+3) miles per hour. If the trip upstream took half an hour longer than the trip downstream, how many hours did it take to make the trip downstream?

A. 2.5

B. 2.4

C. 2.3

D. 2.2

E. 2.1

The way I tried to solve this problem was by setting (90)/(v-3) = (90)/(v+3) + 0.5. Then, I can solve for v but that would take a long time. I could also use the answer choices to solve for v, and then test it using the equation but that seems to take just as long. Is there a better way?


Discussed here:
difficult-ps-problem-help-100767.html

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Re: Faster way to solve this rates problem?   [#permalink] 25 Aug 2011, 05:27
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