Question

A teacher wants to compare the mean geology scores of two different classes. She is testing the null hypothesis that there is no difference in the population mean scores of the two classes. The difference of the sample means is 51.4. If the standard deviation of the distribution of the difference of sample means is 16.66, what is the 95% confidence interval for the population mean difference? A)between -33.2 and + 33.2 B)between -49.9 and +49.9 C)between -102.8 and +102.8 D)between -154.2 and +154.2

Answer 1

Add them together first

Answer 2

A) - 33.2 and + 33.2

Explanation:

When you calculate a confidence interval, there is a rule that a confidence interval of 68% represents the interval from the mean - 1 st. dev. to the mean + 1 st. dev. 95% confidence interval is represents a interval from the mean - 2 st. dev. to the mean +2 st. dev. and 99.7% is the same but +-3 st. dev

In this problem with 95% you have 2 st. dev = 2 * 16.6 = 33.2