Refer to Exercise 7.93. The package of Sylvania CFL 65-watt replacement bulbs that use only 16 watts claims that these bulbs have an average life of 8000 hours. Assume that the lives of all such bulbs have a normal distribution with a mean of 8000 hours and a standard deviation of 400 hours. Find the probability that the mean life of a random sample of 25 such bulbs is
a. Less than 7890 hours
b. Between 7850 and 7910 hours
c. Within 130 hours of the population mean
d. Less than the population mean by 150 hours or more

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