"There is a simple rule how to determine if a number is divisible by three.
Add up the digits and see if the sum of those digits (a much smaller number) is divisible by three.
This rule simplifies finding out if a big number is divisible by three, by reducing it to a small number.
Why is this proposition true?
Consider, for simplicity, a 3 digit number 'abc", such as 321.
Suppose that a+b+c is divisible by 3.
Our number, written as 'abc' is actually
100a+10b+c.
For instance, 321 = 100*3+10*2+1.
Let's rewrite 100a+10b+c as 99a+a + 9b+b + c.
99a+a + 9b+b + c = (99a + 9b) + (a + b + c)
The first part is always divisible by 3 since numbers with all nines are always divisible by 3 (9 = 3*3, 99=33*3, 999=333*3 etc).
That the second part (a+b+c) is divisible by 3, is a given.
So, we have a sum of two parts, both of which are divisible by 3. This sum is, therefore, also divisible by three. Theorem proven."
~http://www.algebra.com/algebra/homework/divisibility/lessons/divisibility-by-3-three.lesson~
By tautology. If it did not work, it would not be a divisibility rule!
why does the divisibility rule work for 4
there is a divisibility for 24 the rule is you can divide 24 as 6 and 4 i think
The rule for 1 and the rule for 3.
it is divisible by 3 and 9
By tautology. If it did not work, it would not be a divisibility rule!
why does the divisibility rule work for 4
If the rules for 2 and 3 work, the number is divisibale by 5.
It is 3 6 9
there is a divisibility for 24 the rule is you can divide 24 as 6 and 4 i think
By using the divisibility rule for 3, we find that 117 is divisible by 3. That makes it composite.
The rule for 1 and the rule for 3.
the divisibility rule for 2 is: The number is even;the last digit ends with a 2,4,6,8,10, etc.The divisibility rule fir 3 is: The sum of the number is divisible by 3The divisibility rule for 4 is: The last two digits are divisible by 4The divisibility rule for 5 is: The number ends with a 5 or 0The divisibility rule for 6 is: The sum CAN be divisible by 2 and or 3The divisibility rule for 9 is: The sum of the number is divisible by 9The divisibility rule for 10 is : The number ends with a 0
it is divisible by 3 and 9
3 - 31
There is no easy rule for divisibility by 34.
The divisibility rules of 4 and 9 are combined to make the divisibility rule of 36.