If you find something useful on here, it's probably an accident.

Calculating the mean or sum of a set of data, or even counting the set of data for use in other formula is easy with Stat mode, available on both types of calculator.

For example, I will calculate the mean and sum of the following set:

$$\large{\{50,63,54,80\}}$$

1. Enter $$\text{STAT}$$ mode by pressing $$\fbox{MODE}\ \fbox{2}$$.
2. Select $$\text{1-VAR}$$ by pressing $$\fbox{1}$$.
3. Enter the values in the set of data, using $$\fbox{=}$$ to move down to the next cell. Use $$\color{navy}{\fbox{↑}}$$ and $$\color{navy}{\fbox{↓}}$$ to move up and down to correct inaccuracies.
4. Press $$\color{maroon}{\fbox{AC}}$$ to exit the data.

The sum of the data is shown using
$$\color{#A80}{\fbox{SHIFT}}\ \fbox{1}\ \fbox{4}$$ ($$\text{Sum}$$) $$\fbox{2}$$ ($$\sum x$$).

The mean of the data is shown using
$$\color{#A80}{\fbox{SHIFT}}\ \fbox{1}\ \fbox{5}$$ ($$\text{Var}$$) $$\fbox{2}$$ ($$\overline X$$).

The number of values $$n$$ is shown using
$$\color{#A80}{\fbox{SHIFT}}\ \fbox{1}\ \fbox{5}$$ ($$\text{Var}$$) $$\fbox{1}$$  ($$n$$).