A Facebook product manager wants to know if the average number of messages sent by people under age 30 is different from the average number of messages sent by people 30 years old or older.The manager collects data from 40 Facebook users under age 30, and 40 Facebook users 30 years old or older.

A: Choose the hypothesis test that she should use to evaluate if there is a difference in the number of messages sent based on the data collected.

B:She calculates a 95% confidence interval for the difference in number of messages based on the samples for each age group.The confidence interval is (18 texts,42 texts).Is there a statistically significant difference in number of messages sent?

C: What is the average difference in number of texts between the two groups?

D:If both groups were half the size, with the same summary statistics, what would you expect to see in the confidence interval?