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Coin Lines

Stage: 4 Challenge Level: Challenge Level:2 Challenge Level:2


  • A coin is randomly tossed onto a set of parallel lines. If the line separation matches the diameter of the coin, what is the chance that the coin touches a line?
  • And what if the line separation is different ? Double ? Half ?

  • If the lines become concentric circles and the gap between the lines doubles, what is the chance now that the coin touches a line?


An answer might be guessed at but the problem is really about justifying that answer.

Do you have a way of visualising it and could you convince a friend?

If you succeed with that it should be an easy next step to generalise for a coin of any size.