A paint manufacturer made a modification to a paint to speed up its drying time.

Question

A paint manufacturer made a modification to a paint to speed up its drying time. Independent simple random samples of 11 cans of type A (the original paint) and 9 cans of type B (the modified paint) were selected and applied to similar surfaces. The following 98% confidence interval was obtained for 1 - 2, the difference between the mean drying time for paint cans of type A and the mean drying time for paint cans of type B: -2.90 hrs < 1 - 2 < 7.50 hrs What does the confidence interval suggest about the population means? Select one: a. The confidence interval includes 0 which suggests that the two population means might be equal. There doesn't appear to be a significant difference between the mean drying time for paint type A and the mean drying time for paint type B. The modification does not seem to be effective in reducing drying times. b. The confidence interval includes only negative values, which suggests that the mean drying time for paint type A is smaller than the mean drying time for paint type B. The modification does not seem to be effective in reducing drying times. c. The confidence interval includes 0 which suggests that the mean drying time for paint type A is greater than the mean drying time for paint type B. The modification seems to be effective in reducing drying times. d. The confidence interval includes only positive values, which suggests that the two population means might be equal. There doesn't appear to be a significant difference between the mean drying time for paint type A and the mean drying time for paint type B. The modification does not seem to be effective in reducing drying times.

Explanation / Answer

Option A is right

The confidence interval includes 0 which suggests that the two population means might be equal. There doesn't appear to be a significant difference between the mean drying time for paint type A and the mean drying time for paint type B. The modification does not seem to be effective in reducing drying times.

There is a close relationship between confidence intervals and significance tests. Specifically, if a statistic is significantly different from 0 at the 0.02 level, then the 98% confidence interval will not contain 0.If the confidence interval includes 0, that implies you think 0 is a reasonable possibility for the true value of the difference.

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