Question 523930
How many prizes should you expect to be won?  {{{mu=np = 20 * .2 = 4}}}
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How many prizes do you need to be 93% confident you have enough for all winners?
{{{sigma=sqrt(npq)=sqrt(20*.2*.8)=1.789}}}
z[.93](one tailed)=1.476
{{{(x-mu)/sigma=1.476}}}
(x-4)/1.789=1.476 Number of prizes you need = x
x-4=2.64
x=6.64 or 7 prizes you need to be 93% confident.
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Ed