Expected monetary value of an alternative with 0.5 probability of making 500?

Answer 1

It is probability sum,

you have 50% chance of winning this is equal to 0.5*500=250

and

you have a 50% chance of losing, this is equal to 0.5*0=0

Hence, the sum of your chances is

0.5*500 + 0.5*0 = 250