Cube Root Speed Drill

Someone cubes a two-digit number and tells you the result — you name the root in seconds.

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How the trick works
  1. Split the cube into two groups of three digits, from the right: 571 | 787.
  2. The last digit of the right group (highlighted) gives the root's ones digit.
  3. The left group sits between two table cubes: 512 ≤ 571 < 729 ⇒ the root's tens digit is 8. Answer: 83.
New session

Questions per session:

Keyboard: type digits, Enter to check / continue, Backspace to fix, H for the cheat sheet.