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  #1  
Old 12-09-2005, 05:19 AM
evanski evanski is offline
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Default Another Probability Question

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.
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Old 12-09-2005, 07:25 AM
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Default Re: Another Probability Question

Mean: 5 * (9/20)
Variance: 5 * (9/20) * (1 - 9/20) * (20 - 5)/(20 - 1)
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Old 12-09-2005, 07:51 AM
evanski evanski is offline
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Default Re: Another Probability Question

why?
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Old 12-09-2005, 09:02 AM
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Default Re: Another Probability Question

Why not? [img]/images/graemlins/laugh.gif[/img]

Is that a homework question?
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