For each value of d.f. (degrees of freedom), look up the value of Student's t in Appendix D for the stated level of confidence. Then use Excel to find the value of Student's t to four decimal places. Which method (Appendix D or Excel) do you prefer, and why?
a. d.f. = 9, 95 percent confidence
b. d.f. = 15, 98 percent confidence
c. d.f. = 47, 90 percent confidence