> 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.
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.