Sure! Here are the rewritten sentences based on the prompts you provided:

1. **I have fewer friends than Lan.**
-> Lan has more friends than I.

2. **Hoa has fewer pens than Lan.**
-> Lan has more pens than Hoa.

3. **Her sister works more hours than Hoa.**
-> Hoa works fewer hours than her sister.

4. **Workers have more vacations than students.**
-> Students have fewer vacations than workers.

5. **Vietnamese students have fewer days off than American students.**
-> American students have more days off than Vietnamese students.

6. **Tam doesn't type as quickly as she used to.**
-> Tam used to type faster.

7. **I eat less chocolate than she does.**
-> She eats more chocolate than me.

8. **Jack is taller than anyone in the class.**
-> No one in the class is as tall as Jack.

9. **Is this stove better than the one you have?**
-> Do you have a better stove than this?

10. **Ba learns less than anyone else in class.**
-> No one in class learns better than Ba.