Question 471567
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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(cured) =.91 and q = .09
nCx = {{{n!/(x!(n-x)!)}}}
5 dolphins treated  n = 5
P(exactly 4 cured) = 5C4(.91)^4(.09) = 5(.91)^4(.09)= .3086