1. The problem statement, all variables and given/known data Hey all, been having some problem with the rule..technique looks right but doesn't agree with wolfram's calc answer. Doing a moment generating function problem. M(t)=(e^5t-e^4t)/t, Find EX and VARX 2. Relevant equations M'(0)=e(x) and so on.. 3. The attempt at a solution Okay, this is an indeterminate equation.. thats why I had to use this rule.. But my answer keeps getting 9 while wolfram says 9/2, so I need some help here. Ok, using quotient rule, differentiating, I get (5e^5t-4e^4t)/t + (e^4t-e^5t)/t^2. Correct me if Im wrong. I separated the latter part of the equation into ((e^4t-e^5t)/t)(1/t), which then equals to (-1)(1/t) Therefore, I get (5e^5t-4e^4t-1)/t, which is indeterminate again, differentiating both nominators, i get 9. What have I done wrong?