Question

If a boat goes 100 km downstream in 10 hours and 75 km upstream in 15 hours what is the speed of the stream

Answer 1

Given

Distance covered downstream = 100

and time required to cover the distance of 100 km = 10 hours

Thus speed = distance/ time = 100/10 = 10 km/h

But this speed is the combine of speed of boat and current of water

Hence x + y = 10 km/h --------(A)

where x = speed of boat and

y = current of water/ speed of stream

Similarly

Distance covered upstream = 75 km and

and time required to cover the distance of 100 km = 10 hours

Thus

x- y = 75/15 = 5 km/h -------(B)

Subtracting A and B we get,

x + y = 10

x- y  = 5

y = 5/2 =2.5 km/h