A solution that just uses logic:
Think of it as if you were drawing one card at a time.
You draw first card: It can be anything P=1
You draw second card: It has to be the same suit as the first one: There are 51 cards left and 12 are the same suit so P=12/51
Third card: 50 cards left 11 of the same suit: P=11/50
4th card: 49 left 10 of the same suit: P=10/49
These all have to happen so we have to multiply together:
1*12/51*11/50*10/49
