A particular brand of calc. battery is approx. normally distributed with a mean of 80 hrs and a standard deviation of 9 hours.
a) What is the probability that a single battery randomly selected from the population will have a life between 70 & 90 hrs?
P(70<x<90) = ?
b)What is the probability that 4 batteries from the population will have a sample mean life of between 70 & 90 hrs?
c) Reduce the standard deviation from 9 to 7 hrs. 4 randomly selected batteries
s= 10/ sqrt 4=5
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