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Par Gelosia: Medieval Multiplication
How it Works
Par gelosia was a method used to multiply in the Middle Ages. The steps and examples below explain how it is done. For example, to multiply 32 X 3, set up a grid as follows:

  • Multiply the first (or only number in this case) by the farthest right number on the top. e.g., 2 X 3.
  • Note the product of the two numbers in the corresponding box on the grid as indicated by the red number "6" in the example. Keep in mind that if the product is a two digit number, the first digit should be placed above the diagonal line.
  • Multiply the first number on the right by the next number to the left on the top row and enter the number in the next square (to the left on the grid). e.g., as indicated by the red number "9".
  • Sum the number in each diagonal row and enter the total on the bottom line as indicated by the green "9" and "6" in the example. Since this is a simple example, there is nothing to sum, "96" is the total.
Here is a more complicated example.
Perform the steps listed above. Keep in mind that this is still a fairly simple example.

If, for instance, the sum of the diagonal column results in a two digit number, you need to carry the sum as you would in normal addition.
© 2001 Tamara Mazzei. All rights reserved.