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(17) The probability that a smoke alarm of a particular brand is defective is 0.03. A company purchases 60 smoke alarms of this brand for its offices. For these 60 smoke alarms, find (a) the mean and variance of the number of defective smoke alarms; (b) the probability that exactly 11 smoke alarms are defective; (c) the probability that at most 4 smoke alarms are defective