Math 300 , Spring 2002, Day 3, Fri, Feb 1 Hit reload to get most current version

Reading: Review 1-2. Read 1-3
"Combinatorics", continued
HW:
Start a page of "Named Probability Distributions."
The first is the Hypergeometric (not in Ash):  If you have n objects, and k are "defective", and you take a sample of r of the objects:  What is the probability of getting 0, 1, 2,...defectives in your sample?
Write down the general formula for x defectives.
    What limitations are there on x  if k < r?  Is there any case where it is impossible for x to be 0 (it is impossible to get no defectives?)  Explain.

"Matching" problems: Can usually be made into a "slot" problem.  If you want to match two sets of individuals, make one set into a labeled "row" of slots (fixed order) and then distribute the other set.

Sometimes it will make a problem easier to "see" if you put labels on the things.

E.g. Musical chairs.  5 kids and 3 chairs. How many ways can they sit down (Oh, in the game they're in a fixed row,  harder.  Assume they're running across the room toward the chairs.)  Chairs 1__, 2__, 3__ .  Kids A, B, C, D, E.  First chair can get any of the 5, then next gets any of the remaining 4, 3rd gets any of the remaining 3.  5x4x3

p. 14:    1, 2, 3,
4 (There's an easy way to do part b.  You get to choose which woman gets handed her coat first, second, etc.  The probabilities will be the same whichever woman you list first.  You can do it other ways but it's harder.)
5,
7 (this is the most complicated one.  But still straightforward)
10, 11


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