A steamer goes downstream from one point to another in 7 hours. It covers the same distance upstream in 8 hours. If the speed of the stream is 2 km/hr, find the speed of the steamer in still water.

Q. A boy walks to his school at a distance of 6 km with constant speed of2.5

\frac{k m}{h r}

and walks back with a constant speed of 4

\frac{k m}{h r}

. His average speed for round trip expressed in

\frac{k m}{h r}

, is

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A boy covers a distance AB of 2 km with speed of 2.5 km/hr, while going from A to B and comes back from B to A with speed 0.5 km/hr, his average speed will be

The correct option is B 0.83 km/hrAs boy goes from A to B and then comes back from B to A, hence his average speed vav=2v1v2v1+v2=2×2.5×0.52.5+0.5=2.53=0.83 km/hr

A boy covers a distance $A B$ of $2 km$ with speed of $2.5 km/hr$ , while going from $A$ to $B$ and comes back from $B$ to $A$ with speed $0.5 km/hr$ , his average speed will be

The correct option is B $0.83 km/hr$
As boy goes from $A$ to $B$ and then comes back from $B$ to $A$ , hence his average speed
$v_{av} = \frac{2 v_{1} v_{2}}{v_{1} + v_{2}} = \frac{2 \times 2.5 \times 0.5}{2.5 + 0.5} = \frac{2.5}{3} = 0.83 km/hr$