An ice cream stand sells three flavors: chocolate, vanilla and bacon. Suppose the popularity of chocolate is p1 and the popularity of vanilla is p2. Find a formula for the probability that among n children, x1 will choose chocolate, x2 will choose vanilla, and the rest will choose bacon.
np1=x1 will chose chocolate
np2=x2 will chose vanilla
n*(1-p1-p2)=x3 will chose bacon