The population of cell phone battery life span is normally distributed with a me

Question

The population of cell phone battery life span is normally distributed with a mean of450 charge cycles with a population standard deviation of 35 charge cycles. a. A single cell phone battery is selected at random. What is the probability that it will have a life span of 400 charge cycles or less? P(400 charge cycles or less) ________ b. ASRS of 50 cell phone batteries is selected determine the probability that it will have an average life span of at least 460 charge cycles? P(mean of at least 460 charge cycles) = _________

Explanation / Answer

1] z= (x-mean)/sigma = 400-450/35 = -1.428

P(z<-1.428) is found from normal tables as 0.076646

2) z = (x-mean)/[sigma/sqrt(n)] = [460-450]/[35/sqrt(50]=2.020

P(z>2.020 is found from normal tables as 0.021692

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