A box in the certain supply room haves ontains seven 40-W lightbulbs, six 60-W bulbs, and four 75-W bulbs. Assume that three bulbs are randomly chosen. (Round your answers to four decimal places.)
(a) Compute the probability that exactly two of the selected bulbs are rated 75-W?
(b) Calculate 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 chosen one by one until a 75-W bulb is found. Determine the probability that it is necessary to examine at least six bulbs?