Grouping multinomial categories. Suppose that counts (N1, . . . Nm) are the rum-bets of results in m categories in n repeated trials. So (N1, . . . Nm) has multinomial distribution with parameters n and
p1, . . . pm as in the box above Example 7. Let 1 < i="">< j="">< m.="" answer="" the="" following="" questions="" with="" an="" explanation,="" but="" no="">
a) What is the distribution of N?
b) What is the distribution of Ni + Nj?
c) What is the joint distribution of Ni, and n - Ni -Nj?