Math practice · reimagined
Rule of three
Turn Rule of three 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
Rule of three
Pick a fighter, choose Rule of three, 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.
Two ratios that match — find the missing piece so they stay in balance.
If 2 apples cost 6 coins, what do 4 apples cost? Apples doubled (2 → 4), so the coins double too → 12. Figure out what you multiplied the first pair by, then do the same to the other.
This is the famous "rule of three." Type the missing number.
More math to master
— Quick answers —
Rule of three: the short FAQ
- Is the Rule of three free to play?
- Yes. The Rule of three 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 Rule of three 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 Rule of three?
- Nope. The Rule of three runs in any browser, and there's a mobile app on the same account if you'd rather train on your phone.
- Can the Rule of three be used in the classroom?
- Absolutely. Teachers run the Rule of three with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.