A random sample of 15 items is drawn from a population whose standard deviation is unknown. The sample mean isx

x= 760 and the sample standard deviation is s= 20. Use Appendix D to find the values of Student'st.

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

The 99% confidence interval is from?? to ??

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

The 99% confidence interval is from?? to ??

(c)Construct an interval estimate ofwith 99% confidence, assuming thats= 80.(Round your answers to 3 decimal places.)

The 99% confidence interval is from ?? to ??