Question

6. A boy takes 4 h to cover certain distance along
the flow and takes 6 h to cover the same distance
opposite to flow. In how much time, he will cross
this distance in still water?
(1) 4.5 h
(2) 5 h
3) 2.4 h
4)4.8 h​

Answer 1

4.8 h will be the answer

Let velocity of man be M

and velocity of water be W

and distance covered be 1 km .

Then,

M+W=1km/4h =0.25

M-W=1km/6h=0.167

equating these two equations we get

M = 0.21

then time taken by man in still water = 1km/0.21=4.76~4.8