Permutations and Combinations

ok so today im going to talk about permutation and combination. In order to do these problems you will need to know a few things.

Permutation is used when you need to find out how many different ways something can be ordered when order is important! The formula for Permutation is:

• nPr = n!/(n-r)!

Combination is used when you need to find out how many different ways something can be ordered when order is NOT important! The formula for Combination is:

• nCr = n!/(n-r)!r

Now that i have given you some info about this.

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

Bam! all done!