The addition of a new accelerator is claimed to decrease the drying time of latex paint by more than 4%. Several test samples were conducted with the following percentage decreases in drying time:

5.2 6.4 3.8 6.3 4.1 2.8 3.2 4.7

a. Find the sample mean.

b. Find the sample standard deviation.

c. Do you think these percentages average 4 or more? Explain.

(Retain these solutions to use in Exercise 9.28, p. 490.)