A random sample of 13 items is drawn from a population whose standard deviation is unknown. The sample mean isx

x= 950 and the sample standard deviation iss= 10.

(a)Construct an interval estimate ofwith 99% confidence.(Round your answers to 3 decimal places.)

The 99% confidence interval is fromto

(b)Construct an interval estimate ofwith 99% confidence, assuming thats= 20.(Round your answers to 3 decimal places.)

The 99% confidence interval is fromto

(c)Construct an interval estimate ofwith 99% confidence, assuming thats= 40.(Round your answers to 3 decimal places.)

The 99% confidence interval is fromto

(d)Describe how the confidence interval changes as s increases.

• The interval stays the same as s increases.
• The interval gets wider as s increases.
• The interval gets narrower as s increases.