The speed of a boat in still water is $8$ km/hr and speed of the stream is $3$ km/hr. Find time taken by boat to go $30$ km upstream.

2

hrs

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7

hrs

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3

hrs

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6

hrs

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Solution

The correct option is D $6$ hrs
speed of the boat= $8 k m / h r$
speed of the stream= $3 k m / h r$
If the speed of the boat in still water is $x k m / h r$ and speed of the stream is $y k m / h r$ then $s p e e d u p s t r e a m = (x - y) k m / h r$
Therefore $s p e e d u p s t r e a m = 8 - 3 = 5 k m / h r$
$d i s t a n c e = 30 k m$
$t i m e = \frac{d i s t a n c e}{s p e e d}$
$\Rightarrow t i m e = \frac{30}{5}$
$\Rightarrow t i m e = 6 h r s$

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