TABLE 7-4 The Lifetimes of a Certain Brand of Light Bulbs Are

question 117

Essay

TABLE 7-4
The lifetimes of a certain brand of light bulbs are known to be normally distributed with a mean of 1,600 hours and a standard deviation of 400 hours. A random sample of 64 of these light bulbs is taken.
-Referring to Table 7-4, the probability is 0.15 that the sample mean lifetime is more than how many hours?

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