# Expectation i.e. ‘E[X]’ in Words

Apr 8, 2021

A **Random variable** is a variable whose **value** **is determined** by some **random event**. The **Expectation of random variable** ‘X’ i.e. E[X] is the **central tendency** of X when **picked once randomly** from the **sample space** (i.e. a homogeneous/ heterogeneous space of all possible outcome).

- E[X+c] = ?

So, E[X+c] = E[X] + c

2. E[cX] = ?

So, E[cX] = c.E[X]

3. E[*X*+*Y*]=?

So, E[*X*+*Y*]=E[*X*]+E[*Y*]

4. Why E[XY] = E[X] * E[Y]?

5. What is Linearity of Expectation?

6. Conditional Expectation?