SOLUTION: Over a long period of time a certain drug has been effective in 75% of the cases in which it has been prescribed. If a doctor is now administering this drug to five patients, what

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Question 813316: Over a long period of time a certain drug has been effective in 75% of the cases in which it has been prescribed. If a doctor is now administering this drug to five patients, what is the probability that it will be effective for three of them (P(x=3) )?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 
Hi,
Note: The probability of x successes in n trials is:
P = nCx* p%5Ex%2Aq%5E%28n-x%29 where p and q are the probabilities of success and failure respectively.
In this case p= .75 & q = .25
nCx = n%21%2F%28x%21%28n-x%29%21%29
P(3 out of 5) = %285%21%2F3%212%21%29%28.75%29%5E2%28.25%29%5E2 = .2637