Question
A boat takes 20 hours to go 200 km upstream. If the boat
doubles its speed, it can cover 200 km downstream in 4 hours. Find the speed of the stream.Solution
Upstream speed of the boat = 200 ÷ 20 = 10 km/h Let speed of the boat in still water = 'x' km/h and speed of the stream = 'y' km/h. So, x - y = 10 ...... (I) Downstream speed when doubled = 200 ÷ 4 = 50 So, 2x + y = 50 ......... (II) Adding (I) and (II): 3x = 60 x = 20 Then, 20 - y = 10 y = 10 Speed of the stream = 10 km/h
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