I'm wondering what is the fastest way to multiply numbers? For now, let's focus on 2-digit numbers and were one cannot use scrap paper.
I've come across 3 fast methods:
60x43 + 4x43 (note that 60x43 is actually a 1-dig. times 2-dig problem) 2580 + 172 = 2752
64x43 = 60x40 + 4x3 =2412 + 4x40 +3x60 = 340 =2752
64 x43 =----- (4x3) (4 from 64) 12 (6x3)+(4x4) (cross multiply) 34 (6x4) 24 ------------+ 2752
*I am aware to some multiplications can be done faster with specific tricks, for example if we square a number, if one of the numbers ends with 5 or is equal to 11, or if they both end in the same number, or if one is close to a multiple of 10, or if one is a product of two 1 digit numbers, etc. But my question regards the general case.
Now practice makes perfect, but before I start training one method I would like to know which one is to be preferred. Is there someone who can say something useful about this? I guess method 3 is not ideal, since the speed of doing the cross multiplication is partly because of the way it is denoted in this example (one above the other). So can someone say whether method 1 or 2 is to be preferred in sense of speed/simplicity?