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?