Negative variance:

"Suppose a box has 5 red balls and 5 blue balls, you choose 2 balls. If the balls are same color, you get $1.10, if balls are different color, you lose $1.00. Find Var(X)"

So E[X] = -0.6/81.
Just accept it, E[X] can be negative.

Then Var(X) = E[X^2] - E[X]^2
which turns out to be negative for me.

If my variance turns out to be negative, do I take the absolute value of it, or have I done a miscalculation 100%?

Question

Negative variance:

"Suppose a box has 5 red balls and 5 blue balls, you choose 2 balls. If the balls are same color, you get $1.10, if balls are different color, you lose $1.00. Find Var(X)"

So E[X] = -0.6/81. 
Just accept it, E[X] can be negative.

Then Var(X) = E[X^2] - E[X]^2
which turns out to be negative for me.

If my variance turns out to be negative, do I take the absolute value of it, or have I done a miscalculation 100%?

mhchen · Answer

My work for variance:
|dw:1570469349195:dw|

As you can see it's negative.

mhchen · Answer

Since E[X^2] can be negative, and E[X]^2 is always positive,
then negative - positive is still negative.

mhchen · Answer

I found my mistake lol.

Summation of X^2 is always positive.