Summary of permutations, combinations and probability
Last updated: 18 Jul 2007
You should remember the following
- Permutations
-
Permutations are where order does matter
`text{Permutations} = (n!)/(n-r)!`
- Combinations
- Combinations are where order does not matter
`text{Combinations} = (n!)/(r!(n-r)!)`
- Basic rule of probability
-
When each possibility is equally likely.
`P(text{outcome}) = text{number of ways it can happen} / text{total number of outcomes}`
- 'And' probabilities
- The probability of two independent outcomes both occurring can be found by multiplying their individual probabilities together.
`P(text{A and B}) = P(A) xx P(B)`
- 'Or' probabilities
- The probability that either of two exclusive outcomes will occur can be found by adding their individual probabilities together.
`P(text{A or B}) = P(A) + P(B)`
Further reading
If you found any part of this tutorial difficult then you may want to study further.
- Probablity lesson from the GMATClub.com
- GMAT probability in perspective from GMAT Daily Tips
- Probability from Math Goodies