9.37 Two different types of coating for pipes are to be compared with respect to their ability to aid in resistance to corrosion. The amount of corrosion on a pipe specimen is quantified by measuring the maximum pit depth. For coating A, 35 specimens showed an average maximum pit depth of 0.18 cm. The standard deviation of these maximum pit depths was 0.02 cm. For coating B, the maximum pit depths in 30 specimens had a mean of 0.21 cm and a standard deviation of 0.03 cm.

Estimate the true difference between mean depths in a 90% confidence interval. Do you think coating B does a better job of inhibiting corrosion?