Menu


Aptitude Permutation and Combination


Permutation

In mathematics, permutation is the different arrangement of a given number of things by taking some or all at a time.

Combination

The combination is a way of selecting items from a collection, such that the order of selection does not matter.

Important formula

Let n be a positive integer. Then, factorial n, denoted n! is defined as:

n! = n(n - 1)(n - 2) ... 3.2.1.

Examples:

  1. We define 0! = 1.
  2. 3! = ( 3 x 2 x 1) = 6.
  3. 4! = (4 x 3 x 2 x 1) = 24.

Number of Permutations:

Number of all permutations of n things, taken r at a time, is given by:

permutation

Examples:

  1. 5P2 = (5 x 4) = 20.
  2. 4P3 = (4 x 3 x 2) = 24.

Important result

If there are n subjects of which p1 are alike of one kind; p2 are alike of another kind; p3 are alike of third kind and so on and pr are alike of rth kind, such that (p1 + p2 + ... pr) = n.

Then, number of permutations of these n objects is =

combination






Subscribe with us to get latest topic update






Choose a Language



Connection failed: SQLSTATE[28000] [1045] Access denied for user 'studentdb'@'localhost' (using password: YES)

Subscribe