In 11 minutes, a man can row three-quarters of a kilometre against the current, and in 7 minutes, he can row down the stream. In calm water, the man's speed (in km/hr) is:
A. 2
B. 3
C. 4
D. 5
Answer:D
In 11 minutes, a man can row three-quarters of a kilometre against the current, and in 7 minutes, he can row down the stream. In calm water, the man's speed (in km/hr) is:
A. 2 B. 3 C. 4 D. 5
Explanation: Three-quarters of a kilometre can be written as 750 metres.and 675 seconds for 11 minutes.,Upstream rate = 750/675 m/sec = 10/9 m/sec.Downstream rate = 750/450 m/sec = 5/3 m/sec.In calm water, the rate is 1/2 10/9 + 5/3 m/sec = 25/18 m/sec= 25/18 x 18/5 km/hr,a speed of 5 km/hr.