arrgh! well, thats what happens when you try and paste maths type stuff heere. oh wel, sorry about that, but i did it by finding the probablity of getting zero, one two and three defectives and determing that:
P(accepted) = P(0) + P(1) x (P(0) + P(1) + P(2)) + P(2) x ((P(0) + P(1)) + P(3) x...