数学练习 · 焕然一新
Series
把Series变成一场你真正想赢的对决。每道题都是一次攻击——解得比对手快，你就命中一击。
4–99+ 岁皆宜 · 无需下载 · 浏览器即玩 · 23 种语言
玩法介绍
Series
选一名斗士，挑选Series，相信你的算力。解得越快越准，出拳就越狠——从轻松的低年级到奥赛级别的挑战，一路升级。
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.
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Series：精简 FAQ
- Series可以免费玩吗？
- 可以。Series在浏览器里就能免费畅玩——课程全部开放，无需下载、无需注册。付费套餐之后才解锁完整斗士阵容、全部场景和进度保存。
- Series适合谁玩？
- 4 到 99+ 岁的任何人。低年级对新手依旧平缓，更高的难度则连自信的玩家也得冒汗。
- 玩Series需要下载什么吗？
- 不需要。Series在任何浏览器里都能跑，笔记本、平板或手机都行。
- Series能在课堂上用吗？
- 当然可以。老师带一整个班玩Series，还能追踪谁在进步——按学生人数计价和教师面板，详见学校套餐。