Some probability terms

[largos]

Is there a difference between mathematical expectation and probability?

// Be well!

[NaobisDad]

Yes there is, and it's not small.

I think you know what a probability is, you are probably just not sure what EV is.

EV for a discrete random variable (X) with values x1 x2 x3 ... xn is defined as:

E(X) = Sum( xi* P(xi). (xi in this case is a value that X can take nad P(xi) is the probability of X taking on that value).

For instance: If you throw a die the probability of it landing on a specific number (xi) is (1/6).

Following from the definition:
EV = E(X) = (1 x 1/6) +(2 x 1/6) +(3 x 1/6) +(4 x 1/6) +(5 x 1/6) +(6 x 1/6) = 3.5


You can think of this as a sort of balancing point in the distribution of possible outcomes. The EV you probably know best is the mean (average). And from it you can make a good common sense explanation of what it means.

I hope you see the clear difference between a probability and EV.

If it's unclear or you need further help, let me know.