Math practice · reimagined
Combinatorics
Turn Combinatorics into a fight you actually want to win. Every problem is an attack — solve it faster than your opponent and you land the hit.
Ages 7–70 · no download · plays in your browser · 20 languages
How it works
Combinatorics
Pick a fighter, choose Combinatorics, and trust your numbers. The faster and cleaner you solve, the harder you hit — from gentle early grades all the way to Olympic-level challenges.
nCk counts how many ways to CHOOSE k things from n when the order doesn't matter — like picking a team, where who's named first makes no difference.
5C2 ("choose 2 from 5") = 10. The formula is n! ÷ (k! × (n−k)!), but the idea is simply: how many different groups can you form?
Type the number of possible groups.
More math to master
— Quick answers —
Combinatorics: the short FAQ
- Is the Combinatorics free to play?
- Yes. The Combinatorics is free to start right in your browser — no download, no signup. Paid plans later unlock the full fighter roster and the deeper curriculum.
- Who is the Combinatorics for?
- Anyone from 7 to 70. The early grades stay gentle for beginners, while the higher tiers will make even the confident sweat.
- Do I need to download anything to play the Combinatorics?
- Nope. The Combinatorics runs in any browser, and there's a mobile app on the same account if you'd rather train on your phone.
- Can the Combinatorics be used in the classroom?
- Absolutely. Teachers run the Combinatorics with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.