MULTIPLICATION BY TWELVE

To multiply any number by 12, you do this:

Double each number in turn and add its neighbor.

This is the same as multiplying by 11 except that now we double the “NUMBER” before we add its “neighbor”. If we wish to multiply 413 by 12, it goes like this:

First step:          0 4 1 3  x  1 2 = _ _ _ 6     double the right-hand figure and carry it down (there is no neighbor)

Second step:      0 4 1 3  x  1 2  = _ _ 56      double the 1 and add 3

Third step:         0 4 1 3  x  1 2  =  _ 956      double the 4, add the 1

Last step:          0 4 1 3  x  1 2   =  4956       zero doubled is zero; add the 4

The answer is 4,956. If you go through it yourself you will find that the calculation goes very fast and is very easy.

Try one yourself:63,247 times 12.  Write it out with the figures spaced apart, and put each figure of the answer directly under the figure of the 63,247 that it came from. This is not only a good habit because of neatness, it also is worth its weight in gold as a protection against errors. In the particular case of speed system of multiplication, we mention it because it will identify the “number” and the “neighbor”. The next blank space in the answer, where the next figure of the answer will go, is directly below the “number” (in this example the figure that you must double). The figure to its right is the “neighbor” that must be added. The example works out in this way:

0 6 3 2 4 7  x  1 2   = _ _ _ _ _ 4     double 7, 14; carry 1

0 6 3 2 4 7  x  1 2   = _ _ _ _ 6 4  double 4, plus 7, plus 1 is 16, carry 1

0 6 3 2 4 7  x  1 2   = _ _ _ 9 6 4 double 2, plus 4, plus 1 is 9

until you end up with: 0 6 3 2 4 7  x  1 2  =  7 5 8 9 6 4