Math practice · reimagined
Series
Turn Series 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
Series
Pick a fighter, choose Series, 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.
A series is what you get when you add a sequence up. Adding evenly-spaced numbers one at a time is slow, and there is a much better way.
The story goes that a schoolboy named Gauss was told to add 1 to 100 and answered almost at once. He had noticed that the numbers pair up from the outside in: 1 + 100 = 101, 2 + 99 = 101, 3 + 98 = 101. Fifty pairs, each worth 101, giving 5050.
The general rule is the same idea: S = n × (a₁ + aₙ) ÷ 2. Read it as "how many terms, times the average of the first and the last", because in an evenly-spaced list the average really is just the midpoint of the two ends.
Add the first and last term, multiply by the number of terms, halve it, and type the sum.
More math to master
— Quick answers —
Series: the short FAQ
- Is Series free to play?
- Yes. Series 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 Series 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 Series?
- Nope. Series runs in any browser, on a laptop, tablet or phone.
- Can Series be used in the classroom?
- Absolutely. Teachers run Series with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.