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If the sum of the digits of a given number equals nine or a multiple of nine, nine is a factor of that number.
No. To find if a number is a factor of 3, add the number's digits. If the resulting number is a multiple of 3, then the original number is a multiple of 3. In 4339, the digits of the number added together is 19, which is not a multiple of 3.
If the last two digits of your target number are a multiple of 4, 4 is a factor of the whole number.
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21 or 35
Oh, dude, a factor of the sum of the digits being 3 or a multiple of 3 just means that if you add up all the digits in a number and it equals 3, or if that sum is a multiple of 3, then that number has a factor that fits the bill. So, like, if you have a number where the digits add up to 3, or 6, or 9, or any multiple of 3, you've got yourself a match! It's like finding a snack in your pantry that fits your cravings perfectly – it just works out, man.
450 or 900
No factor of 9 has three digits. 450 is a three-digit multiple of 150 (and of 9) with a digit sum of 9.
I think you might mean "multiple." If the sum of a number's digits is a multiple of 9, the original number is as well. If you want to know how you know if a number is a factor of 9, memorize the numbers 1, 3 and 9.
The number is 35.
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