Question
You can see if a number is divisible by 2 just by checking to see if it is an
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Hi my name is Bassem Saad, I'm an associate math instructor and a PHD candidate and I'm here today for About.com to introduce some divisibility math tricks.
Divisibility Math Tricks

The first one is actually pretty easy. You can see if the number is divisible by 2 just by checking to see if it is an even number. That's because only even numbers are divisible by 2. That means you'll need to see if the last digit is 0, 2, 4, 6, or 8. For example we have this really big number, but we only need to check to see that it ends in 2.

That means this whole number is divisible by 2. To see if a number is divisible by 3, we have a system. We take the sum of all the digits of the particular number, for example we have 5415, and we want to sum 5 + 4 + 1 + 5. Well this equals 15. Then we check to see if the result is divisible by 3. 15 is divisible by 3, so this whole number is divisible by 3. Finally, the easiest one is to check to see if a number is divisible by 5. We need only to check the last digit to see if it is either 0 or 5. So this number, 17785 is divisible by 5 because it ends in 5.
More Divisibility Math Tricks

So you can combine divisibility tricks to come up with new divisibility tricks. For instance, say we want to know if this number was divisible by 6. Notice that 6 = 2 x 3. So if this number is divisible by 2 and by 3, it's also divisible by 6. So we just check to see first if it's divisible by 2. Notice that it ends in an 8, that means that it's divisible by 2. Then we check to see if it's divisible by 3. So we add 8+7+2+5+8. That equals 30. Well 30 is definitely divisible by 3 so this number is divisible by 6. So now we know a few divisibility math tricks.