Maybe I am getting old, and don't remember how to test numbers for divisibility, but I have learned some really cool tricks that I would like to now share. I will be explaining how to test for divisibility by 2,3, 4,5,6,7,8,and 10. You can find a convenient Divisibility Rules Table here, which I have a printed copy of and have placed on my refrigerator for my step-son that we use quite frequently!
To test a number to see if it is divisible by 2:
You simply look at the last digit in your number, if the last number is any multiple of 2 (0,2,4,6,8) than your number can be divided by 2.
To test a number to see if it is divisible by 3:
You take your given number and add up all the digits, if the sum of digits is a multiple of 3, you have a number that is divisible by 3.
To test a number to see if it is divisible by 4:
You take the last two digits of a number and add them together, if the sum is a multiple of 4, you have a number that is divisible by 4.
To test a number to see if it is divisible by 5:
Check to see if the last digit of given number is a 5 or a 0.
To test a number to see if it is divisible by 6:
Look at the last digit of your given number, decide if it can be a multiple of 2 or 3. For which ever one it is multiple of, you then add up all the digits, if the sum of digits is multiple of 2 or 3, your number is divisible by 6.
To test a number to see if it is divisible by 7:
You will want to subtract 2 times the last digit from the other digits.
224: 22-8=14
To test a number to see if it is divisible by 8:
Check to see if the last 3 digits of your number add up to a sum that is a multiple of 8.
587320 is divisible by 8 because 320 is divisible by 8.
To test a number to see if it is divisible by 9:
Add all the digits of the number in question, check to see if it is a multiple of 9.
To test a number to see if it is divisible by 10:
Look at the last digit in the number you are given, if it ends in 0 than it is divisible by 10.
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