F distribution

In probability theory and statistics, the F-distribution is a continuous probability distribution. It is also known as Snedecor's F distribution or the Fisher-Snedecor distribution (after R.A. Fisher and George W. Snedecor).A random variate of the F-distribution arises as the ratio of two chi-squared variates:where
See more at Wikipedia.org...

The F distribution (for x > 0) has density function (for = 1, 2, ...; = 1,
2, ...):

where
, are the degrees of freedom
(gamma) is the Gamma function.
F Distribution (animation)
The animation above shows various tail areas (p-values) for an F distribution with both degrees of freedom equal to 10.