Chi-Squared help

Can anyone help me? I've been trying to connect all the elements need below, but I just cant!

Can anyone tell me how chi-squared and the F-distribution are related?

Also, what is the mathematical relationship (how they are equal)?
Ok, lets define some random variables, say x1 and x2. Further let each of these variables have chi-square distributions with degrees of freedom r1 and r2 respectively. Then the random variable z, defined by:

z = (x1/r1) / (x2/r2)

has an F distribution with degrees of freedom (r1,r2).

Note here that a chi-square distribution has one parameter, its degrees of freedom (i.e. r1 or r2). An F distribution has two parameters, the numerator degrees of freedom and the denominator degrees of freedom (i.e. r1 and r2).

You can look up the actual pdf of an F random variable in a mathematical statistics book (or derive it youself). However, the important relationship between chi-square random variables and an F random variable is that given above.

Let me know if this helps. Also, this is a good question to ask a statistician if you have the chance.