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Divide & Conquer!

Division can be daunting, not only for your child but for you, when trying to help him or her with their homework. Well, fear no further, there are ways to check if a number is divisible by any of the numbers between 2 and 9. So, before you spend a great deal of your precious time going through every number known to man, woman, and child, here are a few tricks which will help you breathe a sigh of relief.

A number can be divided by 2 if: it is an even number: 0, 2, 4, 6, or 8.

A number can be divided by 3 if: adding up all its digits gives you a multiple of 3:  210- 2+ 1 + 0, you get 3.  Let’s check. 210 ÷ 3 = 70

A number can be divided by 4 if: the tens place is even, and the ones place is 0, 4, or 8, or if the tens place is odd and the ones place is 2 or 6: 60 has an even number in the tens place (6) and a 0 in the ones place, so it’s divisible by 4. If we test it out, we get 15. 72 has an odd number in the tens place (7) and a 2 in the ones, so it’s also divisible by 4; testing it out gets us 18.

A number can be divided by 5 if: it ends with a 5 or a 0.  85 ends in a 5, so it’s divisible by 5

A number can be divided by 6 if: its digits add up to a multiple of 3 and it is even. The digits of 156 add up to 12 (1 + 5 + 6 = 12), and the number itself is even: if we divide it by 6, we get 26.

A number can be divided by 7 if: doubling the last digit and subtracting it from the rest gives you a multiple of 7. 483 is divisible by 7. We start by doubling the last digit–in this case, 3–giving us 6. Then we subtract 6 from the rest of the digits (the “48” in 483), meaning we get: 48 – 6 = 42

A number can be divided by 8 if: the hundreds place is an even number (including 0) and the last two places make up a multiple of 8, or the hundreds place is an odd number, and the last two places make up a multiple of 4 and an odd number: 7,112 the hundreds place is an odd number (1). The last two places make up 12, which is a multiple of 4 and an odd number (3). If we try dividing 7,112 by 8, we see that this trick works: we get 889. 2,672 has an even number in the hundreds place (6) and a multiple of 8 in the last two places (72), so it should also be divisible by 8. If we try it, we get 334.

A number can be divided by 9 if: the digits add up to a multiple of 9. So, if we try this with 243, we get 2 + 4 + 3 = 9, so it should be divisible. If we try it, we get 243 ÷ 9 = 27.

Now go forth, and divide, and conquer! ( See what I did there J)

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