Complementary subtraction. A #mathtrick for your Saturday evening. #mentalmath #numbersense #math

hey want to learn a math trick of course you do let's do a subtraction trick now sometimes subtraction is really easy if all the numbers on top are larger than all the numbers on bottom you just do your subtraction and it's no problem but what if the numbers on top are actually smaller than the numbers on bottom you might remember from school you have to do something about regrouping we have to think back to those tragic second grade years with our weird haircuts i'm going to suggest we do something different called complementary subtraction chunk your numbers into two digit pairs and rather than think about subtracting smaller numbers minus bigger numbers i just want you to think about the difference between the pairs of numbers 63 and 78 how far apart are they 15 apart take the complement of 15. that is what number plus 15 would make 100 85. now to be allowed to do this we are essentially borrowing 100 from the next pair of numbers so when we take that difference 51 minus 41 is 10 you have to take one away that's nine and so that's our difference between these two numbers 10 985 now you can go out to someone and ask them

Channel: Tim Ricchuiti

Views: 1,498

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Id: AxSesRvzT3E

Length: 0min 59sec (59 seconds)

Published: Sat Dec 18 2021