MULTIPLICATION WITH A DIFFERENCE 73

squares (and therefore the size of the quadrilateral) depend-
ing upon the size of the numbers to be multiplied. Each
square is then bisected diagonally. The next step is to write
one of the numbers along the quadrilateral, allowing one
digit to each square, and in the same way to write the other
number along the right-hand side.

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Now in each small square we write down the product of
the digits along each side of the quadrilateral. Thus in the
first square we write the number 18 (i.e. 3 X6), in the second

 

square 15 (i.e. g3 X 5) and so on until all the squares are filled.
When a product consists of one digit, it is written to the right
of the diagonal bisecting the square. When it consists of two

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