Here are the sentences rewritten in passive voice:

1. Letters are typed by Mary in the office.
2. Help will be given to you by his father tomorrow.
3. Human life has been completely changed by science and technology.
4. The bottle was broken by Peter.
5. English is being learned by them in the room.
6. My mind can be changed by nothing.
7. I was not told about it by anyone.
8. Her telephone number is not known by me.
9. The children will be brought home by my students.
10. A present was sent to me last week.
11. More information was given to her.
12. All the workers of the plan were being instructed by the chief engineer.
13. Tea cannot be made with cold water by them.
14. My books have been taken away by somebody.
15. The meeting will be held before May Day by them.
16. The engine of the car needs to be repaired.
17. The window was broken by the boys, and some pictures were taken by them.
18. A lot of money is spent by people on advertising every day.
19. A story is going to be told by the teacher.
20. A cake is being cut by Mary with a sharp knife.
21. The woman with a red hat was looked at by the children.
22. The victims were provided with food and clothing.
23. English is spoken by people in almost every corner of the world.
24. This machine must not be used by you after 5:30 p.m.
25. The chalkboard is erased by one of the students after class.