Common feeling for me, but that's one of the things that pushes me to practice.

For some reason the Ruby version wouldn't let me use Math::sqrt. Had to do it the long way around.

The descrippption says:

Note: m, n, f, b, c are positive integers, where 0 <= m <= n or m >= n >= 0. m and n are inclusive.

The Ruby sample test assertions have an incorrect test. The working set must be 0 <= m <= n, but one of the tests has m as 10,000 and n as 9,950.