Permutation formula is used to find the number of ways an object can be arranged without taking the order into consideration. To recall, when objects or symbols are arranged in different ways and order, it is known as permutation. Permutation can be done in two ways,
- Permutation with repetition: This method is used when we are asked to make different choices each time and with different objects.
- Permutation without Repetition: This method is used when we are asked to reduce 1 from the previous term for each time.
Formulas for Permutations
The formulas for repetition and non-repetition permutation are as stated below:
|Formulas to Calculate Permutation|
|Permuation Formula||nPr = n! / (n−r)!|
|Permutation with Repetition Formula||nPr = nr|
Permutation and Combination
Solved Examples Using Permutation Formula
Question 1: Find the number of permutations if n = 9 and r = 2.
Given n = 9 and r = 2.
Permutation = nPr = n!/ (n−r)!
= 9! /(9-2)! = 9! /7!
Thus, the number of permutations = 72
Question 2: Find how many ways you can rearrange letters of the word “BANANA” all at a time.
Given word: BANANA
Total number of letters in “BANANA” = 6
Total number of “A”s in the word “BANANA” = 3
Total number of “N”s in the word “BANANA” = 2
So, the permutation = (6!)/(3!2!) = (6 × 5 × 4 × 3!)/ (3!2!) = 60