Stating any assumptions that you make, find an expression for the probability that in a group of n people at least two of them share the same birth month. Deduce the smallest n for which the group is more likely than not to include at least two people with the same birth month.

So I think the probability of two people having the same birth month is 1/12 x 1/12 = 1/144 so from that I thought the expression might be:
nP2/144 ? Meaning smallest n would be 10. Teacher said that was wrong though? Stats is really confusing me, can anyone help me out?