## Probability

Posted by mtwinkle on June 6, 2007

1. If there are x people and x seats then total

x!

2. If x people and x seats in a cirlce then total

(x-1)!

3. If x person, x seats, d duplicates, then total

x! / d!

4. If 3 men to be chosen from 8 men then 8C3

5. If x people and y seats, and order matters(permutation) ==> xPy

1. * ^{n}P_{n}* =

*n*!

**2. ** * ^{n}C_{n}* = 1

**3. *** ^{n}C_{r}* =

*(symmetrical property)*

^{n}C_{n-r}**4. *** ^{n}C_{1}* =

*n*

**5.** * ^{n}P_{1}* =

*n*

6. nCr = n! / (r!)(n-r)!

7. nPr = n!/(n-r)!

8.

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