Maurizio T. answered • 04/04/15

Stat PhD passionate about probability and experienced at teaching it.

One simple approach is to consider that there are 2 grey males (M1, M2) and 5 grey females (F1, F2, .. , F5).

If you form all grey couples with these 7 mice, the possibilities are

M1M2, M1F1, M1F2, M1F3, M1F4, M1F5, M2F1, M2F2, M2F3, M2F4, M2F5 i.e, 11 possible cases

The only case that fits your requirement (two males) is M1M2, i.e., 1 case

Thus the probability that both are males give that both are grey is 1/11.