Question 766123: speed of water in certain river is 6kmph and it takes a boat four times as long to row up as to row down the river. what is the speed of boat in still water?
Answer by subudear(62)   (Show Source):
You can put this solution on YOUR website! Let speed of water in river be u kmph
Let speed of boat in still water (water not moving) be v kmph
then time taken by boat to row DOWN the river will be
t*(v + u) = d ...(1)
t = time taken to row down, speed of boat will be (u+v) as flowing water will help boat go fast, d=distance traveled down stream
Similarly time time taken by boat to row UP the river will be
4t*(v - u) = d .....(2)
t = time taken to row UP which is 4 times the time taken to row DOWN, speed of boat will be (v - u) as flowing water will slowdown the boat, d=distance traveled down stream
As distance is same so equating both equations
t*(v + u) = 4t*(v - u)
This gives 5*u = 3*v
Now it is given that water speed is 6 kmph which means u = 6 kmph
substituting the value we get
v = 10 kmph
Speed of boat in still water is 10 kmph
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