The speed at which a man can row a boat in still water is 15 km/hr. If he rows downstream, where the speed of current is 3 km/hr, how many seconds will he take to cover 100 meters?
Choose the most appropriate option.
A) 14  B) 16  C) 18  D) 20  E) 22

Rationale: the speed of the boat downstream = 15 + 3 = 18 km / hr 18 km / hr * 5 / 18 = 5 m / s the time taken to cover 100 meters = 100 / 5 = 20 seconds . the answer is d .
Answer: D