Permutation and Combination

Permutation and Combination is section 15-3. We use Permutation when something is important. We use Combination when something is not important.

Formulas:

• Permutation: nPr = n!/(n-r)!
• Combination: nCr = n!/(n-r)!r!

Example 1: In how many ways can a team with 10 members choose 3 different captains?

• Since it says different in the question, we know that it is important. We will use permutation.
• nPr = n!/(n-r)!
• 10P3 = 10!/(10-3)! = 10!/7! = 10 x 9 x 8 = 720

Example 2: In how many ways can you choose 4 marbles from a bag of 20 marbles if the color does not matter?

• Since the question says "does not matter", we know that we should use combination.
• Formula: nCr = n!/(n-r)!r!
• 20C4 = 20!/(20-4)!4! = 20!/16!4! = 20 x 19 x 18 x 17/4 x 3 x 2 x 1 = 116280/24 = 4845

That is it for this section.

-Amber :)