In mathematics a combination is a way of selecting several things out of a larger group, where (unlike permutations) order does not matter. In smaller cases it is possible to count the number of combinations. For example given three fruit, say an apple, orange and pear, there are three combinations of two that can be drawn from this set: an apple and a pear; an apple and an orange; or a pear and an orange. More formally a k-combination of a set S is a subset of k distinct elements of S. If the set has n elements the number of k-combinations is equal to the binomial coefficient
which can be written using factorials as whenever, and which is zero when . The set of all k-combinations of a set S is sometimes denoted by .
Combinations can refer to the combination of n things taken k at a time without or with repetitions. In the above example repetitions were not allowed. If however it was possible to have two of any one kind of fruit there would be 3 more combinations: one with two apples, one with two oranges, and one with two pears.
With large sets, it becomes necessary to use more sophisticated mathematics to find the number of combinations. For example, a poker hand can be described as a 5-combination (k = 5) of cards from a 52 card deck (n = 52). The 5 cards of the hand are all distinct, and the order of cards in the hand does not matter. There are 2,598,960 such combinations, and the chance of drawing any one hand at random is 1 / 2,598,960.
Read more about Combination: Number of k-combinations, Number of Combinations With Repetition, Number of k-combinations For All k, Probability: Sampling A Random Combination
Famous quotes containing the word combination:
“So of the three methods: reason, sense, or a knowing combination of both, the last seems the least like a winner, the second problematic; only the first has some slim chance of succeeding through sheer perversity, which is possibly the only way to succeed at all.”
—John Ashbery (b. 1927)
“We attempt to remember our collective American childhood, the way it was, but what we often remember is a combination of real past, pieces reshaped by bitterness and love, and, of course, the video past—the portrayals of family life on such television programs as “Leave it to Beaver” and “Father Knows Best” and all the rest.”
—Richard Louv (20th century)
“[The pleasures of writing] correspond exactly to the pleasures of reading, the bliss, the felicity of a phrase is shared by writer and reader: by the satisfied writer and the grateful reader, or—which is the same thing—by the artist grateful to the unknown force in his mind that has suggested a combination of images and by the artistic reader whom his combination satisfies.”
—Vladimir Nabokov (1899–1977)