I know this is an old message but since no-one else seems to have responded I figured I would give my interpretation of what is happening here. I believe the part that says you have 100% chance of success and 20% chance of great success means you have 100% chance of receiving a reward and 20% chance of a higher reward. Basically the results that say you failed at studying are still considered a success because they still awarded points and the results where you successfully study are the great successes that happen 20% of the time. As for studying with Mom, that is a separate activity with a separate reward. Basically you have the choice to study with Mom and get a consistent reward or study alone and probably get a lower reward but have a chance at (or use exploits to guarantee) a higher reward.