Christmaths: a maths advent calendar for CBSE Class 9 and 10 students

The calendar

Each door opens at 00:00 UK time on its day.

1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24

Practice doors

Three sample puzzles, open now, so you (and your teacher) can see how it works. They don't score points.

Leaderboards

The rules

1. A new door opens every day from 1 to 24 December 2026, at 00:00 UK time. That is the same moment for everyone, wherever you are; the calendar shows it in your own time zone.
2. Anyone can open any door that is open and try the puzzle. No calculator: every puzzle works by hand, as in CBSE board exams, and every answer is exact.
3. Sign in to score. A right answer on your first try scores 10 points; on your second try, 5 points; on your third try, no points. You have 3 tries per door.
4. Points count only on a door's own day, until the next door opens at midnight UK time. Then the answer and a full worked solution appear, and you can still try the puzzle for fun.
5. Your streak is the number of days in a row you have solved the door on its own day.
6. If your teacher turns on Christmaths for your class, you appear on a class leaderboard that only your class and its teachers can see, with your first name and initial.
7. The leaderboard for everyone shows nicknames only, and only if you choose a nickname and opt in. Never use your real name. Coming top earns bragging rights.
8. The competition closes at 00:00 UK time on 25 December. The final leaderboards are then frozen, and all 24 doors stay open as a free puzzle archive.
9. Play fair: work the puzzles out yourself. Answers are checked by computer.

For teachers: a Christmas maths competition for your class

Turn on Christmaths for a class in one click: open the class from your teacher dashboard, go to Settings, and tick Christmaths. Your students then appear on a class leaderboard that only the class and its teachers can see, showing first names and initials. Try the practice doors above to see the puzzles' style before December.

Students need to be signed in with the account they use for your class. Nothing else changes for the class.

About Christmaths

Christmaths has 24 Christmas maths puzzles for CBSE Class 9 and 10 Maths, from a gentle warm-up on 1 December to a real challenge on Christmas Eve. Each one has a short hint on how to think about it, a single exact answer and a full worked solution, revealed the day after the door opens.

Want more problems like these all year? Try competition maths.