From a normally distributed population, a simple random sample of size 30 is taken. The mean of the sample is 144 and the standard deviation of the sample is 12.

Which interval is the 90% confidence interval for the population mean?

(142.4, 145.6)

(143.3, 144.7)

(140.4, 147.6)

(139.7, 148.3)

Question

From a normally distributed population, a simple random sample of size 30 is taken. The mean of the sample is 144 and the standard deviation of the sample is 12.

Which interval is the 90% confidence interval for the population mean?

(142.4, 145.6)

(143.3, 144.7)

(140.4, 147.6)

(139.7, 148.3)

justjm · Answer

Complete a *T interval* (because population standard deviation is not given) of x̄=144, s=12, n=30, and C-level = 0.9. You cannot do a z-interval since population standard deviation is not given.

I just use the t interval function on my calculator, but feel free to look up the formula and use the standard probabilities for t distributions.