Expectation and variance of a random variable
Let be a random variable with the following probability distribution:

Value of
-30 0.25
-20 0.05
-10 0.25
0 0.20
10 0.25

Find the expectation and variance of .

Expectation value= -30 *0.25 -20*0.05-10*0.25 +0*0.20 +10*0.25 = -8.5

Variance can be calculated as = (-30 + 8.5)^2*0.25 + (-20+8.5)^2 * 0.05 .

I'll leave that to you to calculate !