I will assume you are rolling 2 dice ....
prob(2,3,4,or 5) 1/36 + 2/36 + 3/36 + 4/36 = 5/18
prob(6,7,or8) = 5/36 + 6/36 + 5/35 = 8/18
prob(9,10,11 or 12) = 4/36 + 3/36+ 2/36 + 1/36 = 5/18
expected value = (5/18)(3) - (8/18)(15) + (5/18)(5) = $ -4.44
Bad game, don't play it
Suppose you win $3 if you roll a sum of 2,3,4, or 5, you lose $15 if you roll a sum of 6,7, or 8, and you win $5 if you roll a sum of 9,10,11, or 12. Find the expected value (mean of the probability distribution) of how much you win or lose for the game.
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