Permutation-Combinations Workshop for CAT

Factorial
Let n be a positive integer. Then, factorial n, denoted n! is defined as:
n! = n(n - 1)(n - 2) ... 3.2.1.
Solved Examples:
i. We define 0! = 1.
ii. 1! = 1.
iii. 4! = (4 x 3 x 2 x 1) = 24.
iv. 5! = (5 x 4 x 3 x 2 x 1) = 120.


Difference between Permutation & Combination
In English we use the word "combination" loosely, without thinking if the sequence/order of things is important or