Discussion of Question with ID = 096 under Boats-and-Streams

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Question

A man can row at $2{2/5}$ km/h in still water and finds that it takes him thrice as much time to row up than as to row down the same distance in the river. The downstream speed of the man is?

A

$3{3/5}$ km/h.

B

$5{3/4}$ km/h.

C

$1{6/7}$ km/h.

D

$4{5/7}$ km/h.

Soln.
Ans: a

If the distance travelled is D and the speed of the current is R km/h, we have $D/{12/5 - R}$ = 3 × $D/{12/5 + R}$. Cancelling D, and solving for R, we get R = ${6/5}$ km/h. So downstream speed would be ${6/5}$ + $12/5$ = $3{3/5}$ km/h.


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