. A box contains six 40-W bulbs, five 60-W bulbs, and four 75-W bulbs. If bulbs are selected one
by one in random order, what is the probability that at least two bulbs must be selected to obtain
one that is rated 75 W?
. Human visual inspection of solder joints on printed circuit boards can be very subjective. Part of
the problem stems from the numerous types of solder defects (e.g., pad nonwetting, knee
visibility, voids) and even the degree to which a joint possesses one or more of these defects.
Consequently, even highly trained inspectors can disagree on the disposition of a particular
joint. In one batch of 10,000 joints, inspector A found 724 that were judged defective, inspector
B found 751 such joints, and 1159 of the joints were judged defective by at least one of the
inspectors. Suppose that one of the 10,000 joints is randomly selected.
(a) What is the probability that the selected joint was judged to be defective by neither of the
two inspectors?
(b) What is the probability that the selected joint was judged to be defective by inspector B but
not by inspector A?