Statistics
posted by Jason L .
It is known that the amount of time needed to change the oil in a car is normally distributed with a standard deviation of 5 minutes. A random sample of 100 oil changes yielded a sample mean of 22 minutes. Compute the 99% confidence interval estimate of the mean of the population.
Also determine the necessary sample size if you wish to be 99% confident and can tolerate an error of 1 minute.
Formula:
CI99 = mean + or  2.575(sd divided by √n)
...where + or  2.575 represents the 99% confidence interval using a ztable, sd = standard deviation, √ = square root, and n = sample size.
With your data:
CI99 = 22 + or  2.575(5/√100)
Finish the calculation for your confidence interval estimate.
Formula for the second part:
n = [(zvalue * sd)/E]^2
...where n = sample size, zvalue will be 2.575 using a ztable to represent the 99% confidence interval, sd = 5, E = 1, ^2 means squared, and * means to multiply.
Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.
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