At an ordinary rate a man can row the distance from

Question

Pasig to Manila, about 15km, in 5 hours less time than it
takes him to return. Could he double his rate, his time to
Manila would only be one hour less than his time to
Pasig. What is the rate of Pasig River?

Answer 1

If his rowing speed is r, and the river's speed is s, then since time = distance/speed,
15/(r+s) = 15/(r-s) - 5
15/(2r+s) = 15/(2r-s) - 1
Now just solve for s.