A data set contains the observations 5, 1, 3, 6, 8. Find 2.

A data set contains the observations 4, 3, 2, 1, 8. Find .

What is the difference between the two above questions regarding the symbols? I know is the sum of the set, but is one squared and one multiplied by two? This is hindering me because I cannot proceed to answer questions like:

A data set contains the observations 4, 6, 5, 7, 1. Find - .

Without knowing proper methods to answer the previous questions.