A lake contains 4 types of fish ,Suppose each fish caught is equally likely to be any one of these types.
Let Y be the number of fish that need ti be caught in order to obtain at least one of each type.
Q1:What is the distribution of Y?
Q2:Give an interval(a,b)such that P(a<Y<b)>0.9

i think it like "negative binominal"
but the probility of each time is difference,
so, anyone help me?