a2zinterviews

17.	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 of 10 km/hr. If the river flows at the speed of 4 km/hr, which of the two friends will return to place A first?
	A.  5.4 km /hr
	B.  7.2 km /hr
	C.  8.4 km/hr
	D.  9.6 km /hr

Solution

Clearly, the cyclist moves both ways at a speed of 12 km/hr. So, average speed of the cyclist = 12 km/hr. Average speed = (2x14x6/14+6) km/hr = 42/5 kmph = 8.4 kmph Since the average speed of the cyclist is greater, he will return to A first.

18.	If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is
	A.  4.2 Km /hr
	B.  9 Km /hr
	C.  13 Km /hr
	D.  21 Km /hr

Solution

Rate upstream = (7/42x60)kmph = 10 kmph. Speed upstream = 3 kmph. Let speed in still water be x km/hr. Then, speed upstream = (x - 3) Km/hr. ∴ x - 3 = 10 or ‹=›x = 13 Km/hr.