The life span of a battery is normally distributed with a me

The life span of a battery is normally distributed with a mean of 2400 hours and a standard deviation of 60 hours. What percent of batteries have a life span that is more than 2490 hours? Would it be unusual for a battery to have a life span that is more than 2490 hours? Explain your reasoning. What percent of batteries have a life span that is more than 2490 hours? Approximately % of batteries have a life span that is more than 2490 hours. (Round to two decimal places as needed.) Would it be unusual for a battery to have a life span that is more than 2490 hours? Explain your reasoning. It is unusual for a battery to have a life span that is more than 2490 hours because the z-score is within 2 standard deviations of the mean. It is not unusual for a battery to have a life span that is more than 2490 hours because the z-score is not within 2 standard deviations of the mean. It is not unusual for a battery to have a life span that is more than 2490 hours because the z-scor

Solution

Normal Distribution
Mean ( u ) =2400
Standard Deviation ( sd )=60
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
a)
P(X > 2490) = (2490-2400)/60
= 90/60 = 1.5
= P ( Z >1.5) From Standard Normal Table
= 0.0668                  
6.68% batteries have a life span that is more than 2490 hours

b)
About 95% of the area under the normal curve is within two standard deviations of the mean. i.e.
(u ± 2*s.d)
(2400+2*60)
(2280, 2520)
2490 is lies in the interval.

It is not unusual for a battery to have a life span that is more than 2490 hours because the z-score is within 2 standard deviations of the mean.