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The speed of a boat in still water is 8 km/hr. If it can travel 20 km down stream at the same time as it can travel 12 km upstream, the rate of stream (in km/hr) is

Answer:

Explanation:

Let rate of stream $=x$ km/hr

Speed of boat in still water $=8$ km/hr 

Upstream speed $=(8-x)$ km/hr

Downstream speed $=(8+x)$ km/hr

Given, $\frac{20}{( 8 + x )}$ $=\frac{12}{( 8-x )}$

$\Rightarrow 160-20x$ $=96+12x$

$\Rightarrow 32x$ $=64$ $\Rightarrow x$ = 2 km/hr.