r-Combinations

A subset of size r is called anr-subset. Counting the number of ways to choose r number of items from a set when order does not matter is called anr-combination.

The counting rules for sequences and subsets are commonly referred to as "permutations and combinations". The term "combination" in the context of counting is another word for "subset"

1.How many five card hands are made entirely of "red" cards?

A five-card hand is just a subset of 5 cards from a deck of 52 cards.

The "red cards" consist of the 13cards from the"diamonds" suite and 13 cardsfrom the"hearts" suite