Question

A motor boat covers the distance between the two sponts on the river 9h and 13 h downsream and upstream respectively. find the time required by the boat to cover this distance in still water.

Answer 1

Let speed of still water be u km/hr and speed of stream be v km /hr.

Let the distance to be covered be x km.

Time taken while travelling downstream = x/ u+v = 9 h ..... (1)

Time taken while travelling upstream = x/ u-v = 13 h ...... (2)

Dividing (1) and (2)

u-v/u+v = 9/13

13u - 13v = 9u + 9v

4u = 22v

v = 2u/11

Substituting for v in (1)

11x / 13u = 9

x = 117u /11

Time taken to cover x distance in still water

= x/u = 117/11 hrs = 10.6 hrs