I'm having a hard time understanding the difference in t distributions and normal distributions when it comes to calculating the statistics.

Infants, even newborns, prefer to look at attractive faces compared to less attractive faces (Slater, et al.,1998). In the study, infants from 1 to 6 days old were shown to photographs of womens faces.Previously a group of adults had rated one of the faces as significantly more attractive than the other.The babies were positioned in front of a screen on which the photographs were presented. The pair offaces remained on the screen until the baby accumulated a total of 20 seconds of looking at one or theother. The number of seconds looking at the attractive face was recorded for each infant.

Number of Seconds Spent Looking at Attractive Face

8

10

12

12

13

13

15

17

17

Question 2) Use the dataset above to calculate each of the following statistics for number of seconds spent looking at attractive face:

a) Mean of the sample b) Estimated standard deviation of the population c) Standard error of the sampling distribution