Why in the numerator is it (13 3) and not 13x12x11?
Alan_Mendoza: Feb. 5, 2015, 11:02 p.m.
There are 13 values of cards and you need to pick 3 of them to be doubled (i.e. your hand could consist of something like 2,2,5,5,9,9). In this case, order does not matter.
weisbart: Feb. 6, 2015, 8:33 p.m.
That's right Alan_Mendoza, you just need to pick four values, the order in which you pick the four values is not relevant to the problem since you are picking them all at once.