SOLUTION: The boat travels 35 km upstream and then back again in 4 h 48min. If the speed of the boat in still water is 15 km/h, what is the speed of the current?
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Question 25489: The boat travels 35 km upstream and then back again in 4 h 48min. If the speed of the boat in still water is 15 km/h, what is the speed of the current? Answer by Paul(988) (Show Source):
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48 min --->0.8h
Speed of the boat with the water = x+15
Speed of the boat against a water = x-15
Total distance = 35
Total time = 4.8h
35[(x-15)-(x+15)]=4.8[(x-15)(x+15)]
35(-30)=4.8(x^2-225)
-1050=4.8x^2-1080
4.8x^2-30=0
4.8x^2=30
x^2=6.25
Square root it.
x=2.5
Hence the speed of the current is 2.5km/h.
Paul.
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