Combination and Permutation

Okay, so this week I am going to explain how to work problems using combination and permutation. This is extremely easy. First your going to need to know a few things.

• You use combination when order does't matter
• You use permutation when order does matter
• The formula for combination is nCr = n!/(n-r)!r!
• The formula for permutation is nPr = n!/(n-r)!
• Another way to work these problems out is by using the combination or permutation function in your calculator.
• n is always going to be the bigger number, while r is always going to be the smaller number in the word problems.

Okay, so now that you know all that you need to know i guess ill work a few examples for you.

example 1: In how many ways can a club with 13 members choose 4 different officers?

• Since the officers are all different then you should automatically know that you are going to be using permutation because the order is important.
• 13 is going to be n and 4 is going to be r.
  
• 13P4 = 17,160

example 2: In how many ways can a 20 person student council choose a two person governing council?

• Since the two person governing council can be anyone, then the order isn't important which means you are going to be using combination
• 20 is going to be n and 2 is going to be r
• 20Cr = 190

and that is how you work problems using combination and permutation. I told you is was easy. well thats it for this week. byeeee

--halie

•