Number Wizardry Unleashed: Dive into Divisibility Tricks Beyond the Basics! 🎩✨
Mr. Kandov, Contributor
January 1, 2024
I’ve always been fond of numbers and how they work.
For example, you probably know that a number ending in 0,2,4,6,8 is even, and therefore divisible by 2.
You may also know that a number ending in 0,5 is divisible by 5 and a number ending in 0 is divisible by 10.
But did you know that the digits of a number also come in handy? For example, the digits of 495 are 4,9, and 5. If you add up the digits and the sum is divisible by 9, then the entire number is divisible by 9 (like 495: 4+9+5 = 18; since 18 is divisible by 9, then so is 495). In fact, you can even cross out any multiples of 9 as you go along for crazy big numbers.
Here’s one: 4925385. Do you think it’s divisible by 9? Mentally, I’ve removed the “4” and “5” and also the “9” because they’re quick sums of 9. We’re left with 2,3,8,5 which sum to 18 (a multiple of 9). Do you see where I’m going with this? Practice this trick on a friend of yours.
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A fun one is checking divisibility by 11. Essentially, you’re doing a similar thing by adding the digits…except here, you’re adding up every other digit (one sum for the first set, and another for the second set).
For instance, 412632: 4+2+3 = 9 and 1+6+2 = 9. Since they match up, the number 412632 is divisible by 11.
Can you find a neat trick for a divisibility check by 3 (easy)? 6 (medium)? Or 7 (evil level)?
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