1. ## mean and variance

If X1, X2, and X3 are independent and have the means 4, 9, abd 3 and the variances 3, 7, and 5, find the mean and the variance of
(a) Y = 2X1 - 3X2 +4X3;
(b) Z = X1 + 2X2 - X3

Also, could someone tell me how to write the subscript using proper mathematical notation on this website? Thanks!

2. Originally Posted by TheHolly
could someone tell me how to write the subscript using proper mathematical notation on this website? Thanks!
type

Y = 2X_1 - 3X_2 +4X_3

Then highlight it, and press the sigma button in the editor (between the php button and the youtube button)

This will "wrap" math tags around your code, which tells the site to read it as Latex syntax.

It will display like this
$\displaystyle Y = 2X_1 - 3X_2 +4X_3$

You could also just type the tags, which is what I usually do.

I attached a picture to show you what it should look like when done.

3. Originally Posted by TheHolly
If X1, X2, and X3 are independent and have the means 4, 9, abd 3 and the variances 3, 7, and 5, find the mean and the variance of
(a) Y = 2X1 - 3X2 +4X3;
(b) Z = X1 + 2X2 - X3

Also, could someone tell me how to write the subscript using proper mathematical notation on this website? Thanks!
All the formulas you need are here.