5 people were asked about the time in a week they spend in doing social work in their community. They replied 10, 7, 13, 20 and 15 hours, respectively. Find the mean time in a week devoted by them for social work.

The enrollment of a school during six consecutive years was as follows:

1620, 2060, 2540, 3250, 3500, 3710.

Find the mean enrollment.

Find the mean of the first twelve natural numbers.

Find the mean of the first six prime numbers.