Just continuing from the post above.... Classical probability - number of relevant events divided by total number of events: . One event is choosing 5 cards from a 52 cards deck. Relevant events are those where you ensure that all 5 cards will be of heart suit. So you isolate heart suited cards. From 13 of them you choose 5. There are ways to do that. Now total number of events is the number of ways to choose 5 from 52: . Divide those two and you have your probability.