Question

A boat travels $30km$ upstream in a river in the same period of time as it takes to travel $50km$ downstream. If the rate of stream be $5kmph$, find the speed of the boat in still water.

Answer 1

Let the speed of boat be $(x-5)$ in upstream and $(x+5)$ in downstream

$s=\frac{d}{t}$ or $t=\frac{d}{s}$

$\Rightarrow \frac{30}{5}=6$hours and $\frac{50}{5}=10$hours

then the equation will be $6(x+5)=10(x-5)$

$6x+30=10x-50$

$\Rightarrow 10x-6x=30+50$

$\Rightarrow 4x=80$

$\Rightarrow x=\frac{80}{4}=20$

speed of the boat in still water is $20$kmph

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