An incoming lot of silicon wafers is to be inspected for
defective ones by an engineer in a
microchip manufacturing plant. Suppose that in a tray containing 24
wafers 6 are defective. Two
wafers are to be selected randomly for inspection. Find the
probabilities of the following events.
a. Neither is defective.
b. At least one of the two is defective.
c. Neither is defective, given that at least one is not
defective.
d. Answer answer the same three questions, assuming this time that
only 3 among the 24
wafers are defective.
a) P(neither is defective) = 18C2/24C2 = 0.5543
b) P(At least one is defective) = (6C1 * 18C1 + 6C2)/24C2 = 0.4457
c) P(neither is defective | at least one is not defective) = 18C2/(6C1 * 18C1 + 18C2)
= 0.5862
d)i) P(neither is defective) = 21C2/24C2 = 0.7609
ii) P(At least one is defective) = (3C1 * 21C1 + 3C2)/24C2 = 0.2391
iii) P(neither is defective | at least one is not defective) = 21C2/(3C1 * 21C1 + 21C2) = 0.7692
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