The lifetimes of certain kinds of electronic devices have a mean of 300 hours and standard deviation of 25 hours. Assuming that the distribution of these lifetimes, which are measured to the nearest hour, can be approximated closely with a normal curve (a) Find the probability that any one of these electronic devices will have a lifetime of more than 350 hours. (b) What percentage will have lifetimes of 300 hours or less? (c) What percentage will have lifetimes from 220 or 260 hours?
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