Math Tip #2 - Simple Divisibility Tests for BIG numbers

How do you tell if a number is divisible by a certain number, such as 2? By using simple divisibility tests, of course!

To check whether a number is divisible by 2 - Pathetically easy, all even numbers are divisible by 2.

To check whether a number is divisible by 3 - Sum up the numbers again and again until you get either 3, 6 or 9. Other answers means that the number isn't divisible by 3.

Examples: 456 4+5+6=15 1+5=6 456 is divisible by 3
124 1+2+4=7 124 isn't divisible by 3

To check whether a number is divisible by 4 - Take the last 2 digits. if the last 2 digits are divisible by 4, the whole number is divisible by 4.

Examples: 424 24 is divisible by 4, therefore 424 is divisible by 4
235 35 is not divisible by 4, therefore 235 is not divisible by 4

To check whether a number is divisible by 5 - Another easy one. Numbers which end with 0 or 5 are divisible by 5

To check whether a number is divisible by 6 - If a number is divisible by 2 AND 3, then the number is divisible by 6.

To check whether a number is divisible by 7 - This is a hard one, but there are a few methods to test whether a number is divisible by 7. This is one way. Reverse the number you want to test, like for 36687, turn it into 78663. Multiplying them successively by the digits 1, 3, 2, 6, 4, 5, repeating with this sequence of multipliers as long as necessary. 7(1)+8(3)+6(2)+6(6)+3(4). If the result is divisible by 7, the number is divisible by 7. In this case, 36687 is divisible by 7. It's easier to just use the calculator...

To check whether a number is divisible by 8 - It's easy, just check whether the last 3 digits is divisible by 8 or not. If it is, the whole number is divisible by 8

To check whether a number is divisible by 9 - Sum up all the numbers. If the result is divisible by 9, the whole number is divisible by 9.

To check whether a number is divisible by 10 - Pathetically easy. All numbers which end with 0 is divisible by 10.

Math Fun Fact #2 - The Magic Square

A magic square has all its rows, columns and diagonals sum up to a same number, and that's what make it magic. But do you know that there is more than meets the eye in a magic square?

Read the rows as numbers forward and backward. You should get this interesting equation if you rearrange them.
816² + 357² + 492² = 618² + 753² + 294².
You will get a similar result if you do the same, but for this time the columns.
834²+ 159² + 672² = 438² + 951² + 276².