IBPS Clerk Prelims 2015 Paper

(a) Speed upstream 'b' = 750m / 775 sec = 30/31 m/sec
Speed downstream 'a' = 750 m/ (15/2)minutes [1 min=60sec] a = 750m/450 sec =5/3 m/sec speed in still water
= ½ (a+b)
= ½ (750/450 + 750/675 ) m /sec
= ½ (750/450 + 750/675 ) × 18/5 km/hr
= ½ (5/3 + 30/31 × 18/5 km/hr
= 4.7 km/hr