According to the rules, you should say: Tom is a slower (adjective) eater than I; Tom eats more slowly (adverb) than I. But in real life conversation, most native speakers "borrow" the adjective and use it as an adverb: Tom eats slower than I. If you are doing college-level work, you might want to use "correct" English. (P. S. And most native speakers even in writing say, "than ME." So many pe