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Fermi Bounder

Bracket the answer before computing. Trains magnitude sense and confidence calibration.

How it works

  • You see a multi-digit expression like 173 × 47
  • Enter lower and upper bounds you're confident contain the true answer
  • You score on containment (did the bracket capture the truth?) AND tightness (narrower is better)
  • 10 problems per round. Tightness target tightens as you go.

Tip: the goal is calibration, not precision. A bracket that's too tight and misses scores worse than one that's wide and contains the truth.