mehrasa wrote:In a given river, the current is 6 mph. A certain riverboat can travel 18 mph in still water. How far upstream (against the current) can the boat travel if a round trip is to take 10 hours?
A) 24
B) 48
C) 60
D) 80
E) 96
Rate upstream = 18-6 = 12 miles per hour.
Rate downstream = 18+6 = 24 miles per hour.
We can plug in the answers, which represent the distance.
Answer choice C: 60 miles.
Time upstream = 60/12 = 5 hours.
Time downstream = 60/24 = 15/6 hours.
Total time = 5 + 15/6 = 45/6 = 7.5 hours.
The time needs to increase by 1/3:
7.5 + (1/3)(7.5) = 10.
Thus, the distance must increase by 1/3:
60 + (1/3)60 = 80.
The correct answer is
D.
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