If the digits of a number add up to a number divisible by three, it's divisible by three.
Ex. Is 4,895 divisible by 3?
4+8+9+5=26
26 is not divisible by 3
No.
Is 246 divisible by 3?
2+4+6=12
12 is divisible by 3
Yes!
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Being Divisibel by 3 and 31
It is divisible by any of its factors which are: 1, 3, 31 and 93
If the rules for 2 and 3 work, the number is divisibale by 5.
26
You have to use the rules of 4 and 9 Using the rules of 2 and 18 won't work because the smallest common multiple of 2 and 18 is 18 not 36. 3 and 12 won't work either because the smallest common multiple of 3 and 12 is 12 not 36. However 4 and 9 does work because their biggest common divisor is 1 so multiplying them works. The biggest common divisor of 2 and 18 is 2 and the biggest common divisor of 3 and 12 is 3
3 and 9. And they divide into 123456789 whether or not you use divisibility rules!
Yes.
Being Divisibel by 3 and 31
Divisibility rules help you find the factors of a number. Once you've found the factors for two or more numbers, you can find what they have in common. Take 231 and 321. If you know the divisibility rules, you know that they are both divisible by 3, so 3 is a common factor.
If a number is divisible by 3 and 5, it is divisible by 15.
The divisibility rules for a prime number is if it is ONLY divisible by 1, and itself.
3 x 3 x 31 = 279
It is divisible by any of its factors which are: 1, 3, 31 and 93
If the rules for 2 and 3 work, the number is divisibale by 5.
With the common divisibility rules, you can quickly see that it is divisible by 5, and by 9 (3 x 3). If you divide 225 by each of these numbers, you should be able to get the remaining factors quickly, as well.
3+7=10
26