A friend of mine recently posted this trick for subtracting any number from any multiple of . (I discovered this trick when I was a boy and have been using it ever since.)
Pedagogically, I don’t think I’d recommend requiring every elementary school student to learn this trick. But this does make a nice enrichment activity for talented elementary school students, as it requires conceptual understanding of subtraction and not just the ability to follow a procedure.
Here’s another approach, taken from the comments of the above webpage: consider 5000 as 500 groups of 10 and 0 groups of 1, and then regroup.
Joseph Nebus
/ February 6, 2016Yeah, that does make the problem a lot easier, doesn’t it?