PSAT #1, Section 4, #20

The key here is to translate that frequency distribution into a set of numbers you can enter into your calculator. The graph tells you that the set contains one 0, one 1, one 2, three 3s, etc. The full set:

{0, 1, 2, 3, 3, 3, 4, 4, 6, 7, 8, 10}

There are 12 numbers in the set, so to find the mean (another word for average) we add them all up and divide by 12: