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A boat covers 48 km upstream and 72 km downstream in 12 hours, while it covers 72 km upstream and 48 km downstream in 13 hours The speed of stream is :
Answer & Solution
Correct Answer:
Option
A
Let downstream speed be D and Upstream speed be U. Then
$$\eqalign{
& {\frac{{48}}{U} + \frac{{72}}{D}} = 12\,.\,.\,.\,.\,.\,.\,.\left( 1 \right) \cr
& {\text{and}} \cr
& {\frac{{72}}{U} + \frac{{48}}{D}} = 13\,.\,.\,.\,.\,.\,.\,.\left( 2 \right) \cr} $$
On solving the equation (1) and (2), we get D = 12 kmph and U = 8 kmph Thus, speed of the current
$$ = \frac{{D - U}}{2} = \frac{4}{2} = 2\,{\text{kmph}}$$
On solving the equation (1) and (2), we get D = 12 kmph and U = 8 kmph Thus, speed of the current
$$ = \frac{{D - U}}{2} = \frac{4}{2} = 2\,{\text{kmph}}$$
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Login48 72 12
72 48 13
upstream=72*72-48*48/72*13-48*12=2880/360=8
downstream=48*48-72*72/48*13-12*72=2880/240=12
so current speed of the stream=12-8/2=2km/hr...(ans)