A boatman can row 36 km with the current in the time he would take to row 18 km against it but if the speed of current were 2 km/h more he would row five times as rapidly with the current as against it. What is his rate of rowing in still water?
Explanation:
Let speed of boatman in still water be b and speed of current = r.
Initially,
Speed of boat against the current = b – r
Speed of boat with the current = b + r
Since the boat covers twice the distance downstream as compared to upstream in the same time, it means downstream speed is twice that of upstream speed.
∴ b + r = 2(b - r)
⇒ b = 3r …(1)
Now, when speed of current is increased by 2 kmph, upstream speed is 5 times downstream speed.
∴ (b + r + 2) = 5(b – (r + 2))
⇒ 4r + 2 = 5(2r - 2)
⇒ r = 2 and b = 6 kmph.
Hence, option (d).
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