A man can swim a distance of 360 m in still water in 4 minutes. If the speed of the current is 1 m / sec, how much time will he take to cover the distance of 180 m upstream?

Distance covered by a man by swimming in still water = 360 m
Time taken by man = 4 minutes = 240 seconds
Speed of man = 360/240 = (3/2) m/sec
Speed of stream is = 1 m/sec.

Time taken in upstream
= 180/[(3/2) - 1)]
= 180/(1/2)
= 360 seconds
⇒ Time = 6 minutes

∴ He will cover 150 m upstream in 6 minutes