SOLUTION: #1) A batch of twelve batteries has two that are defective. Two are picked at random from the lot. What is the probability that at least one is defective?

 

Hi

P(defective) 2/12 = 1/6  , P(not defective) = 5/6

Two picked

P(at least one defective) = 1 -P(none defective) = 1-(5/6)^2



Note: The probability of x successes in n trials is: 

P = nCx*  where p and q are the probabilities of success and failure respectively. 

In this case p = 1/6   & q = 5/6.   n = 2