A person, rowing at the rate of 5 km/h in still water,takes thrice as much time in going 40 km upstream as in going 40 km downstream. Find the speed of the stream.
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Let speed of stream be 's'
Let speed of boat in still water be 'b'
Speed of boat in still water = b = 5 km/h
Let time taken by the boat in going 40km downstream be t1 and time taken by the boat in going 40km upstream be t2.
Time = distance/speed
t1 = 40/(b+s)
t2 = 40/(b-s)
He takes thrice as much as time going in 40km upstream as going 40km downstream.
→t2 = 3t1
→40/(5-s) = 3(40/(5+s))
→1/(5-s) = 3[1/(5+s)]
→5+s = 3(5-s)
→5+s = 15-3s
→ s+3s = 15-5
→ 4s = 10
→ s = 10/4
→ s = 5/2
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