Suppose we have two boxes; box 1 contains 4 defective and 16 non defective light bulbs. box 2 contains 1 defective and 1 non defective light bulb. we roll a fair die one time. if we get a 1 or a 2, we select a bulb at random from box 1. otherwise we select a bulb from box 2. what is the probability that the selected bulb will be defective?