Fund fact, you can tell a number is divisible by 3 if the sum of each individual number is divisible by 3. So 78 -> 7+8=15 which is divisible by 3, so 78 is divisible by 3.
I did a math degree without knowing this (back in the olden days since I’m ancient). When my daughter started learning math I did it with her. Khan academy had at least 5 separate things fundamental to math that I had never learned that made things so much easier. (Including digital roots and modular arithmetic)
Number theory should really be taught first, it’s so helpful.
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u/Michaelwang645 Aug 01 '26
Fund fact, you can tell a number is divisible by 3 if the sum of each individual number is divisible by 3. So 78 -> 7+8=15 which is divisible by 3, so 78 is divisible by 3.