[w1ntermute]

Well, that's an example of the time-memory tradeoff, right? It takes a lot longer to calculate 9·7 that way than it does if you've just memorized it. The real question is where to draw the line with respect to diminishing returns on memorizing products for larger and larger numbers.

[vorg]

> where to draw the line with respect to diminishing returns on memorizing products for larger and larger numbers

Everything from 2 * 2 to 9 * 9 where the second number is greater or equal to the first, i.e. 36 combinations. But it would also be good to memorize sums from 3 + 2 to 9 + 8 where the second number is less than the first, i.e. another 28 combinations. So we'd need to memorize 64 combinations from 2,2 to 9,9 where we'd know whether the result is addition or multiplication from the ordering of the numbers.

[fredgrott]

all 9s..in multiplication take second muliplicand subtract one and that is the first digit of the answer..now take that first multiplicand and subtract that first digit of the answer and that is the second digit of the answer

memorizing without knowledge is for chumps!