### 7.4.3 The multinomial probability function: multinomial

If X follows a multinomial probability distribution with P = [p0,p1,…,pj] (where p0 + … + pj = 1), then for K=[k0,…,kj] with k0 + … + kj = n, the probability that X=K is given by the multinomial command;

multinomial(n,P,K)=

n!
k0!k1!… kj!

(p0k0p1k1… pjkj.

You will get an error if k0 + … + kj is not equal to n, although you won’t get one if p0 + … + pj is not equal to 1.

For example, if you make 10 choices, where each choice is one of three items; the first has a 0.2 probability of being chosen, the second a 0.3 probability and the third a 0.5 probability, the probability that you end up with 3 of the first item, 2 of the second and 5 of the third will be

multinomial(10,[0.2,0.3,0.5],[3,2,5])

or

0.0567