1. 

A man can row three-quarters of a kilometre against the stream in 11 minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:
A. 2
B. 3
C. 4
D. 5

Answer: Option D

Explanation:

We can write three-quarters of a kilometre as 750 metres,

and 11 minutes as 675 seconds.

Rate upstream = 750 m/sec = 10 m/sec.
675 9

Rate downstream = 750 m/sec = 5 m/sec.
450 3

Rate in still water = 1 10 + 5 m/sec
2 9 3

   = 25 m/sec
18

   = 25 x 18 km/hr
18 5

   = 5 km/hr.