## Thursday, May 14, 2009

### BOBBY!

I'll start by saying this unit went too fast! But it was pretty straight forward. Many things like the "pick" or "choose" formula are things I might need to remember since I keep forgetting them in class. I'm also really nervous about the word problems. Since Mr.K can dish out some mean word problems xD.

Many things I learned:

1. Permutation is where the order matters. Combination is where the order doesn't. (That's why Mr.K says a combination lock should really be called a permutation lock.) :P

2. When there is a Permutation we use the "pick formula" and when there is a combination we use the "choose formula."

3. The Pick formula is P(n,r) = (n!) / (n-r)!
n= number of objects to pick from
r= how many objects you pick from the total.(order matters)

4. The choose formula is C(n,k) = (n!) / k!(n-k)!
n= number of objects to choose from
k= how many objects you choose from the total. (order doesn't matter)

5. With circular permutations its (n-1)! to find the possibilities.

6. 0! is 1

7. non distinguishable objects = (n!)/(k1!)(k2!)(k3!)..........
for example the word BOB has 2 b's but they look exactly alike so if you wanted to find how many words can be spelled...

3!/2! = 3

8. Bracelets and necklaces are special. You need to divide the result by 2 because it can be flipped over.

This unit will definitely be interesting and I will study hard for this one. There are still many things I need to master before I consider myself an expert on this topic. So hopefully I'm a master by Friday :D.