To tell if a number is evenly divisible by three, add all the digits in it until you arrive at a single digit. For instance, the number 9234 adds up to 18, which adds up to nine. Nine is evenly divisible by three, so 9234 is evenly divisible by three.
Continue ReadingThe trick for three also works for nine, except the final number must be evenly divisible by nine. If a number is even, it is evenly divisible by two. The trick for six is a combination of the tricks for two and three: the number must be even and evenly divisible by six when the digits are added up until a single digit is reached. A digit is evenly divisible by five if the last digit is a zero or a five, while a number is evenly divisible by 10 if the last digit is a zero.
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