a)You have 1/2 probability of getting an even number and a 1/2 probability of getting an odd number. 2 points for even, -3 points for odd.
Even= 1/2 x 2
= 1
Odd = 1/2 x -3
= -1.5
add 1 and /1.5 to get -0.5
b) Not fair because you will lose more points than win.