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There is a road beside a river. Two friends started from a place A, moved to a temple situated at another place B and then returned to A again. One of them moves on a cycle at a speed of 12 km/hr, while the other sails on a boat at a speed oi 10 km/hr. If the river flows at the speed of 4 km/hr, which of the two friends wit return to place A first ?

Answer:

Explanation:

Clearly, the cyclist moves both ways at a speed of 12 km/hr. So, average speed of the cyclist = 12 km/hr.

The boat sailor moves downstream at $(10 + 4)$ $=14$ km/hr

and upstream at $(10 - 4)$ $=6$ km/hr

So, average speed of the boat sailor $=\frac{2\times 14\times 6}{14+6}$ km/hr

$=\frac{42}{5}$ $=8.4$ km/hr.

Since the average speed of the cyclist is greater, he will return to A first.