SOLUTION: Let X be the lifetime of an electronic device. It is known that the average lifetime of the device is 755 days and the standard deviation is 95 days. Let xˉ be the sample mean

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Question 859821: Let X be the lifetime of an electronic device. It is known that the average lifetime of the device is 755 days and the standard deviation is 95 days. Let xˉ be the sample mean of the lifetimes of 204 devices. The distribution of X is unknown, however, the distribution of xˉ should be approximately normal according to the Central Limit Theorem. Calculate the following probabilities using the normal approximation.
(a) P(xˉ≤749)= Answer
(b) P(xˉ≥768)= Answer
(c) P(746≤xˉ≤768)=
Answer by ewatrrr(24785) About Me  (Show Source):
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Hi,

 Calculate the following probabilities using the normal approximation.

m = 755 and s = 95/sqrt(204) = 6.6513

(a) P(x ≤749)= normalcdf( -9999, 749, 755, 6.6513)

 (b) P(x ≥768)= 1 - normalcdf( 768, 9999, 755, 6.6513)

 (c) P(746 ≤x≤ 768)=normalcdf( 746, 768, 755, 6.6513)