When p particular things are always included and q particular things are always excluded n-p-q C r-p. C n r n r. The number of permutations of n objects taken r at a time is determined by the following formula.
N P r n.
When order matters and repetition is allowed if n is the number of things to choose from balloons digits etc and you choose r of them 5 balloons for the party 4 digits for the password etc the number of permutations will equal P nr. And if we expand the formula 8 P 5 8. Well also look at how to use these ideas to find probabilities. 3 5.