B tech. Discrete mathematics (I. T & Comp. Science Engg.) Syllabus

Note: 0!=1
Example 2:

Let’s say you have four friends, but only need to text three of them when order matters. Find the number of ways to text your friends.

Solution:

P(4,3) =

4! ₌ 24 _{= 24}

(4 - 3)! 1!
There are 24 ways to test three out of your four friends if order matters.
Combination Formula:
The permutation of n – things taken r at a time is:

n = the total number of items you have from which to choose r = the number you are actually going to use.

Example 3:

The art club has 4 members. They want to choose a group of three to compete in a regional competition. How many ways can three members be chosen?

Solution:

There are 4 ways to chose 3 people for the competition when order is not important