Yesterday (Tuesday, October 5, 2010) we learned about divisibility rules. Divisibility rules are like little tricks to figure out if a number is divisible by a number. The numbers we learned about were; 2, 3, 4, 5 and 6. Below I will try to explain the rules for these numbers to the best of my ability.
  1. One is simple. Any number can divided by one.
  2. Two is pretty easy, too. If the number ends with an even digit, it can be divided by two.
  3. Three was a little harder. You add up all the digits of the number. So if the number is 32,001, you add up 3, 2 and 1 and get 6. 6 is divisible by 3, so 32,001 is divisible by three.
  4. Four involves memory. If the last digit in the number is even, the digit before it has to be either a 0, 4, or 8. If the last digit is odd, the digit before it has to be either a 2 or a 6. If these rules work with the number, it is divisible by four.
  5. Five is easy. If the last digit ends with a 0 or 5, it is divisible by five.
  6. 2 and 3 have to go into the number
  7. The easiest was is to just divide by7
  8. the last 3 numbers have to be divisible by 8
  9. the digits have to add up to a multiple of 9
  10. the number has to end in 0