Question
Arjun covers a distance of 96 km downstream and then
returns the same distance upstream, completing the entire journey in 7 hours. Given that the speed of the stream is 4 km/h, what is the speed of the boat in still water?Solution
ATQ;
Let boat speed in still water = b km/h
Downstream speed = b + 4
Upstream speed = b – 4
Total time = (96 ÷ (b + 4)) + (96 ÷ (b – 4)) = 7
Checking the factors of 96, (28+4 and 28−4 are both factors)
Check: downstream = 28 + 4 = 32 km/h, upstream = 28 – 4 = 24 km/h
Time = 96/32 + 96/24 = 3 + 4 = 7 hours
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