A man can row three-quarters of a kilometre against the stream in 11 1/4 minutes. The speed (in km/hr) of the man in still water is:  Choose the most appropriate option
A) 4 1/4 km/hr	B) 5 km/hr	C) 6 km/hr	D) 7 km/hr	E) None
Sol.   Rate upstream = [750 / 675] m/sec = 10/9 m/sec.   Rate downstream = [750 / 450] m/sec = 5/3 m/sec.   ∴ Rate in still water = 1/2 [10/9 + 5/3] m/sec = 25/18 m/sec = [25/18 * 18/5] km/hr   = 5 km/hr   Answer 5 km/hr
<result>B</result>
A man can row three-quarters of a kilometre against the stream in 11 1/4 minutes. The speed (in km/hr) of the man in still water is: