Card Flip Magic: Error Detection & Correction

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This magic trick is based on how computers detect and correct data errors. In the trick, a volunteer lays out a 5 x 5 square of identical cards colored on one side, with a random mix of sides showing. The magician adds another row and column, making sure that the extra cards make an even number of colored cards in each row and column. When the volunteer flips over a card, the row and column with the changed card will now have an odd number of colored cards, identifying the changed card. Extension activities further explore the idea of error correction, including its use in book ISBNs.

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
30 to 45 minutes

Estimated Materials Cost:
1 cent - $1 per group of students

Age Range:
Ages 8 - adult

Resource Types:
Activity, Demonstration, Lesson/Lesson Plan

English, French, Greek, Hungarian, Italian, Polish, Portuguese, Russian, Turkish

Materials List (per group of students)

  • A set of 36 “fridge magnet” cards, coloured on one side only
  • A metal board (a whiteboard works well) for the demonstration.
  • 36 identical cards, coloured on one side only.


  • Engineering and Technology
    • Computing
      • Computer Science
    • Engineering
      • Computer Engineering
  • Mathematics
    • Algebra
      • Patterns
    • Data Analysis and Probability
      • Data Representation
    • Representation

Informal Categories

  • Computers


To use this activity, learners need to:

  • see
  • see color
  • touch

Learning styles supported:

  • Involves hands-on or lab activities