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 4–99+ · no download · plays in your browser · 23 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.
— Quick answers —
Rule of three: the short FAQ
- Is Rule of three free to play?
- Yes. Rule of three is free to play right in your browser — the whole curriculum, no download, no signup. Paid plans later unlock the full fighter roster, every stage and saved progress.
- Who is Rule of three for?
- Anyone from 4 to 99+. 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 Rule of three?
- Nope. Rule of three runs in any browser, on a laptop, tablet or phone.
- Can Rule of three be used in the classroom?
- Absolutely. Teachers run Rule of three with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.