Few children (or adults) know more than
one way to multiply numbers.
They have only been taught the method of decimal-offsets, summing the
resulting rows.
Noone ever told them there is another way,
a way which would make them think too (as in: **WHY*** does Stu
Savory's multiplication method work?*)

Here's an example, with just two 2-digit numbers, to keep it simple, but the method works for integers of any size.
Let's assume we want to multiply 43 by 57. That's 2451, you can do that in your head or use a calculator to check it.
Write two columns on a sheet of paper. In row one, write 43 in col 1 and 57 in col 2, as shown here.
In row two, halve col 1 (throwing any remainder away) and double col 2.
Repeat this step until you have a row with a "1" in col 1.
Now copy column two into a third column, except that you write a zero in col 3 for the rows which have an even number in col 1.
Now just add up col three, and *voila* there is the correct result, 2451 in this case!
The method works for integers of any size. Try this
and astound your friends!

Worked Example for 43*57=2451.

43 | 57 | 57 |

21 | 114 | 114 |

10 | 228 | 0 |

5 | 456 | 456 |

2 | 912 | 0 |

1 | 1824 | 1824 |

sum up column three | 2451 |

Now go visit my blog please, or look at other interesting maths stuff :-)

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