Question

a lot consists of 144 ball pens of which 20 are defective. the customer will buy a ball pen if it is good, but will not buy a defective ball pen. the shopkeeper draws one pen at random from the lot and gives it to the customer. what is the probability that customer will buy the ball pen?

Answer 1

non defective pen = 144-20=124
probability = 124/144=31/36