A box in a certain supply room haves three 40-W lightbulbs, seven 60-W bulbs, and six 75-W bulbs. Assume that three bulbs are randomly selected. (Round your answers to four decimal places.)
(a) Determine the probability that exactly two of the selected bulbs are rated 75-W?
(b) Determine the probability that all three of the selected bulbs have the same rating?
(c) Determine the probability that one bulb of each type is selected?
(d) Assume now that bulbs are to be selected one by one until a 75-W bulb is found. What is the probability that it is necessary to examine at least six bulbs?