Re: lottery odds - april 4, 97

["Caleb J. McArthur" <cmcarthu@umich.edu>]

> I made a similiar statement a few weeks ago and someone replied that
> you can't add statiistical probabliities.  You would have to calculate
> the actual probability for the Boston & Dallas pick rather than add
> the two's individual probability.  


Not true here.  Let's say there are 1000 ping pong balls (after we
eliminate Vancouver's and Toronto's) and Boston has 280 and Dallas has 80. 
The chance of a Dallas ping pong ball coming up is 80/1000 or 8%.  The
chance of a Boston ping pong ball coming up is 280/1000 or 28%.  What is
the chance that the first ball will be either a Dallas ball or a Boston
ball?  Well, there are 360 balls that are either Dallas balls or Boston
balls, so the chance is 360/1000 or 36% which equals Boston's chances plus
Dallas' chances.


The simplest way to think of Boston's odds is to ask how many ping pong
balls do we own.  We own all of ours plus all of Dallas'.  Take this
number and divide it by the total number of ping pong balls that are
eligible for the first pick (1000 - Vancouver balls - Toronto balls).

CJM