Question

A boat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is ___ km/hr.

Answer 1

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 - x) km/hr

So we know from question that it took 4(1/2)hrs to travel back to same point.

$So,</p><p>\begin{aligned}</p><p>\frac{30}{15+x} - \frac{30}{15-x} = 4\frac{1}{2} \\</p><p>=> \frac{900}{225 - x^2} = \frac{9}{2} \\</p><p>=> 9x^2 = 225 \\</p><p>=> x = 5 km/hr</p><p>\end{aligned}$

hope it's help you ✔️

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