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# Statistics homework help?

The charge life of a certain battery for cell phones is normally distributed with a mean of 200 minutes and a standard deviation of 40 minutes.

What is the probability that a random sample of 16 of these batteries has an average charge life of less than 180 minutes?

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- 3 weeks ago
The sample is normally distributed with a standard deviation 40/√16 = 40/4 = 10 minutes.

P(x <= 180) = P[(x-200)/10 <= (180-200)/10] = P(z <= -2) = 0.023

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