# Study Notes #3

## 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)
x1
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

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: