Suppose you roll a die and you get whatever comes up (i.e. if I roll a 1 you get 1 dollar, if you roll a 6 you get 6 dollars, etc.). Also consider that you can roll the die once and get the money or you can choose to roll again and get whatever comes up the second time. Which option is better to choose?
So the expected value of the first option is $$\sum x p_x = 3.5$$ What is the expected value of the second option?
Would it be $$x-3.5$$