## Notation and Random Variables

- capital letters – random variables
- lowercase letters with subscripts – individual instances

**Notations**

```
X
A random variable
Example - Time spent on website
(On spreadsheet the column label)
```

`x`_{1}
First observed value of the random variable X. (subscript row number)
Example - 15 minutes

\sum_{i=1}^nx_i

```
Sum values beginning at the first observation and ending at the last value
Example:
5+2+3
```

\frac 1 n \sum_{i=1}^nx_i

```
Sum values beginning at the first observation and ending at the last value and divide by the number of observations (the mean)
Example:
(5+2+3)/3
```

\bar x

```
Exactly the same as the above - the mean of our data.
Example:
(5+2+3)/3
```

## Notes for Spreadsheet

**Range:**

`=A1-AVERAGE(A$1:A$10)`

same with:

x_1-\bar x

```
=C1^2
square root for each data of a data set in spreadsheet
get the average to get the variance
```

```
I think, the formula can also be written as:
=(A1-AVERAGE(A$1:A$10))^2
=AVERAGE(D1:D10)
```

*Testing my theory…*

## Shape and Outliers

*Suggested Reading from my first project’s feedback: *