Question 470656
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Hi,
Note: The probability of x successes in n trials is: 
P = nCx* {{{p^x*q^(n-x)}}} where p and q are the probabilities of success and failure respectively. 
In this case p(CO test) = .8  & q = .2
nCx = {{{n!/(x!(n-x)!)}}}
P(exactly 5 test) = 12C5(.8)^5(.2)^7 = 792(.8)^5(.2)^7 = .0033
P(at least half) = 1 - P(0)-P(1)-P(2)-P(3)-P(4)-P(5)= .9961
Recommend the use of a personal statistical calculator or using the calculators on sites such as: stattrek.com