SOLUTION: From a lot of 12 missiles 5 are selected at random and fired. If the lot contains 3 defective missiles that will not fire, what is the probability that a) all 5 will fire? b) at

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Question 637647: From a lot of 12 missiles 5 are selected at random and fired. If the lot contains 3 defective missiles that will not fire, what is the probability that
a) all 5 will fire?
b) at most two will fire?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi, 

From a lot of 12 missiles, 5 are selected at random and fired. 

If the lot contains 3 defective missiles 1%2F4th are defective

P(5 will fire) = (3/4)^5

P(at most 2 will fire) = P(0 fire) + P(1 fire) + P(2 fire)

                       = %281%2F4%29%5E5+%2B+5%283%2F4%29%5E1%281%2F4%29%5E4+%2B+10%283%2F4%29%5E2%281%2F4%29%5E3



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 = 3/4 & q = 1/4

nCx = n%21%2F%28x%21%28n-x%29%21%29