# Linear combination of gaussian random variables

I know what random variables are but I don't understand what a linear combination of gaussian random variables is. Can anyone please give me an explanation or clues? Thanks in advance, Julien.

A linear combination of Gaussian random variables is another random variable, not necessarily Gaussian itself, that you get by adding and subtracting Gaussian random variables. Lets call this linear combination of Gaussian variables $Y$. The random variable $Y$ could be something like $$Y = 2 \times X_1 + 1.2234 \times X_2 -7$$ Or it could be something like $$Y = \frac{X_1 - 0.01 \times X_2}{12}$$
where $X$'s are Gaussian random variables. As you can see a linear combination of them is obtained by summing them up or subtracting them from each other, but never multiplying or dividing them with each other or by itself (like squaring or taking roots).
We can give general form of linear combination of random Gaussian variables: $$Y = a_1X_1 + a_2X_2 + ... + a_n X_n$$
where $a_i$ is any number you want it to be, like -222, or 0 or 17.222...