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I picked up this trick intuitively as a very young kid, perhaps 7-8 I break multiplication and division up into chunks of 1's, 5's, and 10's so that it's mostl
by gavinray 5y ago
I picked up this trick intuitively as a very young kid, perhaps 7-8
I break multiplication and division up into chunks of 1's, 5's, and 10's so that it's mostly just adding a zero to the end, or doing that and then cutting it in half.
I never learned multiplication tables, long division, lattice multiplication or anything else. just did this in my head.
So say you want to find 86 * 32
86 * 10 = 860
860 * 3 = (2400 + 180 = 2580)
2580 + (86 * 2) = 2752
It starts to break down for bigger numbers depending on how "uneven" they are but it's been pretty useful in general
- brimble 5y agoMultiplication tables memorized in school usually stop at 12x12. They're super useful for doing the exact thing you demonstrated, in your head, very fast, using some tricks to turn the problem into smaller problems (with memorized answers, so they're solved almost instantly). Memorizing that multiplication table was a more valuable use of time than the vast majority of time I spent learning mathematics. It's useful daily. Can't say that for much else.
- xigoi 5y agoHow do you know that 800 × 3 = 2400 if you haven't learned multiplication tables?
- alvarlagerlof 5y agoAddition
- johnaspden 5y ago(8+8+8)*100
- gavinray 5y ago8 x 3 = 24 8 x 300 = 2400 Add two zeros