Don’t know your tables? Never mind, in this system you don’t need them beyond 5 × 5!
- Suppose you need 8 x 7
8 is 2 below 10 and 7 is 3 below 10.
Think of it like this:
The answer is 56.
The diagram below shows how you get it.
You subtract crosswise 8-3 or 7 - 2 to get 5,
the first figure of the answer.
And you multiply vertically: 2 x 3 to get 6,
the last figure of the answer.
That's all you do:
See how far the numbers are below 10, subtract one
number's deficiency from the other number, and
multiply the deficiencies together.
- 7 x 6 = 42
Here there is a carry: the 1 in the 12 goes over to
make 3 into 4.
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