my answer is: ((9 nCr 3)(6 nCr 2)7)/(15 nCr 5) But the answer is ((9 nCr 3)(6 nCr 2)7)/((15 nCr 4)*11) it says that there are (15 nCr 4) ways of choosing the first 4 and 11 ways to choose the 5th. But I don't understand this explaination, I think these two denominator should give the same number, but they don't.

Thanks.