 Casting Out Nines,
a selection of answers from the Dr. Math archives.
 Divisibility Rules  Dr. Math FAQ
 How can you tell whether a number is divisible by another number
(leaving no remainder) without actually doing the division? Why do
"divisibility rules" work?
 From the archives:
 Casting Out Nines to Check Arithmetic
 Can you explain how to use the 'casting out 9's' technique in a way
that a 6th grader can understand?
 Casting Out Nines
 I am trying to find a reference that defines this mathematical operation...
 Casting Out Nines and Elevens
 Why is nine used in proving this math answer?
 When Casting Out Nines Fails
 To prove that casting out 9's worked, I intentionally used an incorrect
quotient, but was shocked when the problem checked out correctly.
 Casting Out Nines  Proof
 Show that if the order of the digits of a natural number is permutated
to form a new number, the difference between the old number and the new
number is divisible by 9.
 Accountants Use 9 to Check for Errors
 I know accountants divide the difference of debits and credits by 9
to check for a transposition error. I need to understand why this works.
 Even or Odd in Base 5?
 Is there a way to find whether a number written in base 5 is even
or odd without first converting it to base ten?
 Sum of the Digits of Multiples of 9
 Why do the digits of nine times a singledigit number add up to 9?
