Consider all n! permutations of the set {1,2,3,..., n}. We say that a number i is a fixed point of a permutation if i appears in the ith position. For example, if n = 3, the permutation {2,3, 1} has zero fixed points, {3,2, 1} has one fixed point, and {1,2,3} has three fixed points. Let pn(k) be the number of permutations of {1, 2, 3, ...,n} that have exactly k fixed points. For example, we have p3(0) = 2, p3(1) = 3, p3(2) = 0, and p3(3) = 1. (a) Suppose n = 4. Determine the values of p4(0), p4(1), p4(2), p4(3), and p4(4).
Permutations and Combinations
If there are 5 dishes, they can be relished in any order at a time. In permutation, it should be in a particular order. In combination, the order does not matter. Take 3 letters a, b, and c. The possible ways of pairing any two letters are ab, bc, ac, ba, cb and ca. It is in a particular order. So, this can be called the permutation of a, b, and c. But if the order does not matter then ab is the same as ba. Similarly, bc is the same as cb and ac is the same as ca. Here the list has ab, bc, and ac alone. This can be called the combination of a, b, and c.
Counting Theory
The fundamental counting principle is a rule that is used to count the total number of possible outcomes in a given situation.
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