A number is a multiple of 312 if it's a multiple of 3, 8 and 13 at the same time
For example 1,248 is a multiple of 312 because 1 + 2 + 4 + 8 = 15, which means it's a multiple of 3, ends in 248, which means it's a multiple of 8, and 124 + 8 x 4 = 156, which means it's a multiple of 13
The rule works because 312 = 2^3 x 3 x 13
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It isn't worthwhile to invent or memorize complicated divisibility rules for lots of numbers. Just carrying out the divisions is faster in most cases.
A number is a multiple of 312 if it's a multiple of 3, 8 and 13 at the same time
Yes. 312 / 3 = 104Because, using your divisibility rules you know that the sum of the numbers (3+1+2) is 6 which is a multiple of 3. threfor you can say, that is does devide by three.
Knowing the divisibility rules will help you by being able to recognize if a number has factors (other than one and itself) which are covered by the rules. This will save actually having to start doing divisions.
If the number is even and the sum of its digits is divisible by nine then the number is divisible by 18.
If the rules for 2 and 3 work, the number is divisibale by 5.