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There are many other combinatorial interpretations of binomial coefficients (counting problems for which the answer is given by a binomial coefficient expression), for instance the number of words formed of n bits (digits 0 or 1) whose sum is k is given by (), while the number of ways to write = + + + where every a i is a nonnegative integer is ...
To refer to combinations in which repetition is allowed, the terms k-combination with repetition, k-multiset, [2] or k-selection, [3] are often used. [4] If, in the above example, it were possible to have two of any one kind of fruit there would be 3 more 2-selections: one with two apples, one with two oranges, and one with two pears.
One must divide the number of combinations producing the given result by the total number of possible combinations (for example, () =,,).The numerator equates to the number of ways to select the winning numbers multiplied by the number of ways to select the losing numbers.
Sloping lines denote graphs of 2x+5y=n where n is the total in pence, and x and y are the non-negative number of 2p and 5p coins, respectively. A point on a line gives a combination of 2p and 5p for its given total (green). Multiple points on a line imply multiple possible combinations (blue). Only lines with n = 1 or 3 have no points (red).
The three-choose-two combination yields two results, depending on whether a bin is allowed to have zero items. In both results the number of bins is 3. If zero is not allowed, the number of cookies should be n = 6, as described in the previous figure. If zero is allowed, the number of cookies should only be n = 3.
A k –elements combination from some set is another name for a k –elements subset, so the number of combinations, denoted as C(n, k) (also called binomial coefficient) is a number of subsets with k elements in a set with n elements; in other words it's the number of sets with k elements which are elements of the power set of a set with n ...
The number of derangements of a set of size n is known as the subfactorial of n or the n th derangement number or n th de Montmort number (after Pierre Remond de Montmort). Notations for subfactorials in common use include !n, D n, d n, or n¡ . [a] [1] [2] For n > 0 , the subfactorial !n equals the nearest integer to n!/e, where n!
The main application of the combinatorial number system is that it allows rapid computation of the k-combination that is at a given position in the lexicographic ordering, without having to explicitly list the k-combinations preceding it; this allows for instance random generation of k-combinations of a given set.