A mental math course

How the course works

Each topic teaches one technique. You see how the trick works, why it is worth knowing and where people usually slip — then practice it right away in a feed you scroll through.

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Multiplying by 5 and 25

  1. To ×5, multiply by 10 and halve; ×25 is ×100 then ÷4; ×50 is ×100 then ÷2.
  2. Why this trick
  3. How it works
  4. Worked examples
  5. Common mistakes
  6. 36·5 in one move: ×10, then halve. What do you get? ×5 = ×10 ÷ 2: 36·10=360, halved = 180.
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A mental math course

39 topics in 7 chapters with 1,334 practice questions.

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