In a poker hand of 5 cards from an ordinary deck of 52 cards, find the probability of getting a full house. Note: a full house is a hand that consists of 3 of one rank and 2 of another.My solution:

$\displaystyle \frac{13{{4}\choose{3}} * 12{{4}\choose{2}}}{{{52}\choose{5}}}$$\displaystyle +\frac{12{{4}\choose{3}} * 13{{4}\choose{2}}}{{{52}\choose{5}}}$

But, for some reason my answer is twice the answer given in the solution.