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It takes 2 hours to travel 20 miles downstream on a cruise s

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It takes 2 hours to travel 20 miles downstream on a cruise s

by Max@Math Revolution » Thu Aug 15, 2019 11:56 pm

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[GMAT math practice question]

It takes 2 hours to travel 20 miles downstream on a cruise ship that travels at a constant speed along a river flowing at a speed of 2 miles per hour. How long will it take for the cruise ship to travel 18 miles upstream on this river?

A. 1 h 30 min
B. 2 h
C. 2 h 30 min
D. 3 h
E. 3 h 30min
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by deloitte247 » Sun Aug 18, 2019 6:24 am
Let the speed of ship = s
For downstream => Distance = speed * time
20 = 2 * (s+2)
20 = 2s + 4
2s = 20 - 4
2s = 16
s = 16/2 = 8 mph

For upstream => Speed of ship against the flow = 8 - 2 = 6mph
Time taken = distance / speed
= 18miles / 6mph = 3 hours

Answer = option D
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by Max@Math Revolution » Sun Aug 18, 2019 5:15 pm
=>

Suppose the speed of the ship is x miles/hr.
Then 20/(x+2) = 2, and x = 8.
The time to taken to travel 18 miles upstream is 18/(8-2) = 18/6 = 3 hours.

Therefore, the answer is D.
Answer: D
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