Combinations

• A combination is an arrangement of a set without regards to order.
• _nPr = n!/(n-r)!
• _nCr = n!/[(n-r)!r!]
• Look at two letter arrangements of {a,b,c}
• Judges in a contest vs Officers in a club.
• P 807 22, 23, 27, 34, 36
• P 813 9-22

Binomial Probability Formula

• If we have an experiment which has a binary outcome (success or failure)
  • Toss a coin, heads or tails.
  • Roll a dice, 1 or not 1
• Let p be the the probability of success.
• Let q = 1-p
• If we conduct the experiment a number of times (n)
• P(x) is the probability that the experiment succeeds x times.
• P(x) = _nCxp^xq^n-x
• Page 822 5-10
• Page 822 11-21