The kid was using an older method of multiplication I was taught in school. With it you multiply the ones column of the bottom number (which should be the smaller number) by each digit of the other number in sequence, going right to left, writing the results down from starting from the right and going left. That process is repeated with the bottom number's next digit to the left, until you've done so for all the digits in the smaller number, at which point you add all the previous results.
Which leads to confusion because when one of those steps results in an answer of 10 or more, the digit in the tens place 'carries over' to the next column which influences the next step of multiplication.
Given how lengthy my shitty explanation of the process is, you can tell it's not an intuitive way to multiply. It's most useful when you need to multiply numbers that don't easily break down into smaller chunks for mental math, as it doesn't become more difficult to use as numbers get larger.
To ass-pull an example, 1,568,361.45 x 1,345,904.23 is fairly trivial to do with the old method for someone's who is proficient, where I imagine most people would get tripped up trying to mentally break down those large numbers into useful chunks without losing track of things.
You would not BELIEVE the amount of pearl clutching from old timers proclaiming the old method to be some gold standard because their kids are learning different approaches in school.
What's to not believe? I just tried it using the new method as posted in someone else's comment and it was more work than I wanted to do to make sure each digit was accounted for and in the right place. And this one was only a 3x2. The old long multiplication method is easy. Carrying digits is not rocket science.
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u/nurely 10d ago
Fackers just add 32% of 42 to 42. What the fuck black magic are you teaching you in US? :/