Question

A boat goes 30 km upstream and 100 km downstream in 6 hours. It takes 2 hours more to travel 90 km upstream and 50 km downstream. How much time will it take to go 50 km downstream and 30 km upstream

Answer 1

Let the speed upstream be A and downstream be B
So from the question:
30/A + 100/B = 6
and 90/A + 50/B = 8
Let 1/A = x , 1/B = y
Hence on solving these two equation, we get x = 1/15 , y = 1/25

So A = 15 and B = 25

So the time taken to go 50 km downstream and 30km upstream is
50/B+ 30/A = 50/25 + 30/15 = 2 + 2 = 4