A man can row three-quarters of a kilometer against the stream in 45/4 minutes and down the stream in 15/2 minutes. The speed (in km/hr) of the man in still water is:

Question: A man can row three-quarters of a kilometer against the stream in 45/4 minutes and down the stream in 15/2 minutes. The speed (in km/hr) of the man in still water is:

Solution:
three - quarters of a kilometer = 750 meters
45/4 minutes = (45/4) × 60 = 675 sec
15/2 minutes = (15/2) × 60 = 450sec


Rate upstream = 750/ 675 m/sec
= 10/9
Rate downstream =750/450 m/sec
=5/3 m/sec


∴Rate in still water= (1/2){(10/9) + (5/3)} m/sec
= (1/2){(10 + 15)/9}
= (1/2)(25/9)
= 25/18
= (25/18)(18/5) km/hr.
= 5 km/hr