Permutation and Combination:

Read the underneath points carefully.

Permutation and combination having little bit difference. Permutation is nothing but arrangement of things where as combination is nothing but selection of things.

In permutation the way of arranging things is affect the result but in combination it won’t affect anywhere.

Example for permutation: The permutation of two letters from group of three letters

AB, BA, AC, CA, BC, CB

Example for combination: The combination of two letters from group of three letters

AB, BC, CA

Formulae:

- n! = 1* 2 * 3 * 4 * 5 * 6……. (n-1) * n
- nc0 = 1
- ncn = 1

Previous year solved Questions:

1. How many ways the letters of the word ‘ARMOUR’ can be arranged?

A) 720 B) 300 C) 640 D) 350 E) None of these

Ans: E

Solution: Total number of letters = 6 and R is repeated twice.

Required arrangements = (6! / 2!) = 360

2. How many ways the letters of the word ‘BANKING’ can be arranged?

A) 5040 B) 2540 C) 5080 D) 2520 E) None of these

Ans: D

Solution: Total number of letters = 7 and N is repeated twice.

Required arrangements = (7! / 2!) = 2520

3. In how many ways, a group of 3 boys and 2 girls can be formed out of a total of 4 boys and 4 girls?

A) 15 B) 16 C) 20 D) 24 E) None of these

Ans: D

Solution: Total number of ways = (select 3 boys from group of 4 boys) * (2 girls from group of 4 girls)

=> (4c3) * (4c2) = 24