Hello tutor I'm having a hard time understand how to identify statistic.

How how do you know if a test statistic is negative or positive? Could you give me some example?

1. The average number of cavities that thirty-year-old Americans have had in their lifetimes is 7. Do twenty-year-olds have a different number of cavities? The data show the results of a survey of 15 twenty-year-olds who were asked how many cavities they have had. Assume that the distribution of the population is normal.

4, 8, 5, 5, 4, 5, 7, 8, 4, 8, 8, 6, 8, 5, 7

The T test statistic =

2. On average, a banana will last 7 days from the time it is purchased in the store to the time it is too rotten to eat. Is the mean time to spoil less if the banana is hung from the ceiling? The data show results of an experiment with 11 bananas that are hung from the ceiling. Assume that that distribution of the population is normal.

5.7, 7.4, 5.5, 8.1, 4.5, 6.6, 6.7, 8.1, 5.9, 7.7, 7.2

The T test statistic =