Multiple regression degrees of freedom $f$-test.

I'm finding conflicting information from college textbooks on calculating the degrees of freedom for a a global $F$-test on a multiple regression. To be absolutely clear, assume there are 50 observations and 3 independent variables. Can you please tell me the df for the numerator and denominator? I have found 2 sets of numbers in college texts. One indicating the numerator is equal to $P$, in this case 3, and alternatively $P-1$. For the denominator I am finding $n-p$,which in this case would be 47, and alternatively, $n-p-1$. Perhaps I am misunderstanding the material and there are circumstances when one vs. the other formula applies. I've not done any regression analysis in more than 25 years and now find I'm stuck on a Christmas vacation project I wanted to do with my son. So any help that would explain, in a gentle way, (I can't get through the quadratic explanation, or something that will bury me in calculus) how to determine the df would be appreciated. Concrete examples would be very beneficial. Also, if there is a good practical walk through of multiple regression/Anova that will show some examples and explain concepts (but please do not recommend Regression for Dummies) I'd appreciate a referral to that as well. Thanks for your help.