Other mistake: After his wife has a party at their house, Thorton Melon (Dangerfield) decides to have a swim in his pool. The camera shows Melon as he is about to dive into the pool from the edge. The camera cuts away and a much "thinner" Melon is seen doing a flip into the water. Watch carefully as the "thinner" man makes his dive. You can clearly see his hairpiece fly off the top of his head.
Other mistake: Rodney Dangerfield dives into the pool to show his son a dive. When he climbs out, he's bone dry!
Answer: We don't know that he answered all the questions right, just that he answered the last one right. Based on Barbay's upset response to that correct answer, it is likely Thornton was at the edge between a wrong answer giving him an F and a correct answer giving him the D he got.
jimba