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evanski
12-09-2005, 05:19 AM
If you have 20 coins, 9 of them quarters and 11 nickels. You select 5 coins at random. What is the mean and variance of the number of quarters selected?

Thanks.

12-09-2005, 07:25 AM
Mean: 5 * (9/20)
Variance: 5 * (9/20) * (1 - 9/20) * (20 - 5)/(20 - 1)

evanski
12-09-2005, 07:51 AM
why?

12-09-2005, 09:02 AM
Why not? /images/graemlins/laugh.gif

Is that a homework question?