Two-Cube Calendar

Each face of two cubes is labeled with a single digit from 0 to 9. It is possible to show any date from 01 to 31 on the front faces. The problem is to determine the sum of the digits that cannot be seen.
See the details for a hint.


  • [Snapshot]
  • [Snapshot]


Each cube must have faces with 0, 1, and 2, leaving six faces with 3, 4, 5, 6, 7, 8; the face with 6 can be turned upside down to be 9.
[1] M. Gardner, The Colossal Book of Short Puzzles and Problems, New York: W. W. Norton, 2006 pp. 4, 18.


    • Share:

Embed Interactive Demonstration New!

Just copy and paste this snippet of JavaScript code into your website or blog to put the live Demonstration on your site. More details »

Files require Wolfram CDF Player or Mathematica.