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A motorboat covers the distance from one pier to the other pier in 4 hours and the way back in 5 hours. What is the speed of the boat in still water, if it covers 70 km with the current in 3.5 hours? (its
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1 vote
A motorboat covers the distance from one pier to the other pier in 4 hours and the way back in 5 hours. What is the speed of the boat in still water, if it covers 70 km with the current in 3.5 hours?

(its not 20 i tried)

User Sunil Agarwal
by
6.3k points

1 Answer

4 votes
r = speed in still water
r + c = speed with current
r - c = speed against current

3.5(r + c) = 70
r + c = 20
c = 20 - r

4(r + c) = distance from pier to pier
5(r - c) = distance from pier to pier
4(r + c) = 5(r - c)
4(r + 20 - r) = 5(r - 20 + r)
80 = 10r - 100
180 = 10r
18 = r
The speed in still water is 18 km/hour
User Benjamin Conant
by
6.0k points
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