Motorola X Bar and confidence intervals
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Motorola wishes to estimate the mean talk time for one of their new phones before the battery must be recharged. In a random sample of 35 phones, the sample mean talk time is 325 minutes.
A) Why can we say that the sampling distribution of x-bar is appropriately normal?
B) Construct a 98% Confidence Interval for the mean talk time for all new motorola phones, assuming that the population standard deviation is 31 minutes.
C) Contruct a 90% Confidence Interval for the mean talk time for all new motorola phones, assuming that the population standard deviation is 31 minutes.
D) How many phones would Motorola need to test to estimate the mean talk time for all new Motorola phones within 5 minutes with a 99% confidence ?
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