A box contains 20 electric bulbs, out of which 4 are defective. Two bulbs are chosen at random from this box. The probability that at least one of these is defective is
Correct Answer : A.
Please remember that Maximum portability is 1. So we can get total probability of non defective bulbs and subtract it form 1 to get total probability of defective bulbs. So here we go, Total cases of non defective bulbs
Total cases probability P of at least one defective