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 2100 hours and a
standard deviation of 60 hours.

A) What percent of batteries have a life span that is more than 2175 hours?

B) Would it be unusual for a battery to have a life span that is more than 2175 hours? Explain your reasoning.

Solution

A) 2175 - 2100 = 75 --> 75/60 = 1.25 standard deviations

since we\'re looking for what percentage of batteries have lifespan above 2175 hours, we want to find the probability that we have a z-value larger than 1.25.

P(z>1.25) = 10.56%

B) No it isn\'t strange because having a z-value of 1.25 is not statistically significant (P<.05)