A, B and C are the three place on a river where B is equidistant from A and C. Monika can row from A to B and back in 9 hours and from A to C in 5 hours. Find the ratio of speed of his boat in still water with that of the current.

9 : 4

Let the distance AC be 2d 

so AB = d

\(\frac{d}{x + y}\) + \(\frac{d}{x - y}\) = 9   ---(i)

\(\frac{2dx}{(x + y)(x -y)}\)  = 9   ---(i)

\(\frac{2d}{x + y}\)  = 5   ---(ii)

Divide (i) by (ii)

\(\frac{x}{x - y}\)  = \(\frac{9}{5}\)

\(\frac{1}{1 - \frac{y}{x}}\)  = \(\frac{9}{5}\)

\(\frac{y}{x}\) = \(\frac{4}{9}\)

or x : y = 9 : 4