Pr(X=xk) = C*r^(xk) for k = 1,2,3,4 where the positive constants C and r can be determined by the requirements that the sum of all the probabilities must be 1 and the expected value must be 2.5.
r^x = e^kx, where e^k=r. So. Would you like to wager whether r=1?
r^x = e^kx, where e^k=r. So. Would you like to wager whether r=1?