1. Tim is younger than Sarah.
2. Your house is smaller than mine.
3. Bill is shorter than David.
4. Jack's marks are worse than mine.
5. This book is more expensive than that one.
6. Your bike is slower than mine.

Sentence 1: Tim is older than Sarah. (young)
 * Analysis: We need to compare Sarah's age to Tim's.
 * Rewritten sentence: Sarah is younger than Tim.
Sentence 2: Our house is larger than yours. (small)
 * Analysis: We need to compare the size of your house to ours.
 * Rewritten sentence: Your house is smaller than ours.
Sentence 3: Bill is not as tall as David. (short)
 * Analysis: We need to compare Bill's height to David's.
 * Rewritten sentence: Bill is shorter than David.
Sentence 4: Jack's marks are worse than mine. (good)
 * Analysis: We need to compare our marks to Jack's.
 * Rewritten sentence: My marks are better than Jack's.
Sentence 5: This book is the same price as that one. (expensive)
 * Analysis: We need to compare the price of the two books.
 * Rewritten sentence: That book is as expensive as this one.
Sentence 6: Your bike is slower than mine.
 * Analysis: The sentence is already in the correct comparative form.