On: The Way You Learned Math Is So Old School

[light3]

Surely that method of multiplication is not suited for larger numbers, to get 246 * 369 u do 200 * 300 200 * 60 200 * 9 40 * 300 40 * 60 40 * 9 6 * 300 6 * 60 6 * 9 So for x-digit multiplied by y-digit u need to write down x*y products and then sum it up, where as for the old method you need to only write down min(x,y) products and sum it up.

[hackerblues → light3]

This is somewhat misleading. Yes, it's true if

    3 * 123456789

counts as one multiplication.

But if you're doing the 'old' version you implement it as 9 single digit multiplications:

    3*9, 3*8,....,3*1

all written down with appropriate carrying.

If you do it with the new method you again get 9 'single' digit multiplications:

    3*9, 3*80, ..., 3*100000000

which you then add up.

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The old methods efficiency comes from writing the steps out in a compact notation, not from reducing the number of multiplications or additions.