Use the Following Information for Questions

Short Answer

Use the following information for questions:
People who go on a (leisure) vacation tend to gain weight. It is thought that the average difference between weight before the vacation and after the vacation is roughly 2 pounds with a standard deviation of 2.5 pounds. Ten vacationing people are to be randomly selected and their weights measured, both upon departure and return of their vacation.
-What is the expected value of the sample mean difference between after and before vacation weight?