A man takes half time in rowing a certain distance downstream than upstream. What is the ratio of the speed…
A man takes half time in rowing a certain distance downstream than upstream. What is the ratio of the speed in still water to the speed of current?
1 : 2
2 : 1
1 : 3
3 : 1
Solution
Let speed in still water be $b$ and speed of current be $c$. Downstream speed $= b+c$, upstream speed $= b-c$. Time is inversely proportional to speed. Downstream time is half the upstream time, so downstream speed is twice the upstream speed: $b + c = 2(b - c)$. This gives $b + c = 2b - 2c$, so $3c = b$, i.e. $b : c = 3 : 1$.