Question

A motor boat whose speed in still water is 5 km/h, takes 1 hour more to go 12 km upstream than to retum downstream to the same spot. Find the speed of the stream

Answer 1

time taken by upstream=time taken by down stream+1

so t'-t"=1

t'=d/(Vb-Vw)

t"=d/(Vb+Vw)

so 1=d/(Vb-Vw)-d/(Vb+Vw)

by solving the above equation we get. (Vw+25)(Vw-1)=0

so velocity of river is 1kmper hour

as itcant be negative.