MathematicsA motor boat in still water travels at a speed of 36kmph. It goes 56 km upstream in 1 hour 45 min. The time taken by it to travel the same downstream is

A motor boat in still water travels at a speed of 36kmph. It goes 56 km upstream in 1 hour 45 min. The time taken by it to travel the same downstream is

A
2 hr 25 min
B
3 hr
C
1 hr 24 min
D
2 hr 21 min

Solution:

Speed upstream

= \frac{56 km}{1 \frac{3}{4} hr}

$= \frac{56 \times 4}{7} = 32 kmph$

Let the speed of the current be $x$ kmph

$∴ 36 - x = 32$

$x = 36 - 32 = 4 kmph$

Speed downstream $= 36 + 4 = 40 kmph$

$∴$ Taken downstream $= \frac{56}{40} = \frac{7}{5} hrs$

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