Tell if a number divides by 3
Add up the digits. If that sum divides by 3, so does the whole number, however long it is.
- Take a number, like 5,412.
- Add its digits: 5 + 4 + 1 + 2 = 12.
- Still big? Add again: 1 + 2 = 3.
- If the sum divides by 3, the number does too. The same test works for 9.
Tip: Handy for splitting a bill three ways: if the total's digits add to a multiple of 3, it splits evenly to the cent.
Try it now: Which of these divide by 3: 471, 1,024, 8,253? (471 and 8,253 do; 1,024 doesn't.)
Next crumbs
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