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STAT 226, Section A—Quiz 10 (4 pts.)
A paint is applied to tin panels and baked for 1 hour so that the mean index of
hardness is 35.2. Suppose 18 test panels are painted and baked for 3 h, producing a
sample mean index of hardness equal to 35.95 and standard deviation 2.2. Assume
here that the distribution of the hardness indexes is normal, regardless of the baking
1. Construct a 98% confidence interval for the mean index of hardness.
2. Is there statistically significant evidence (for a significance level of 2%) that
longer baking does not affect hardness of the paint? Fully justify your answer.