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Casting Out Nines
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Dr. Math FAQ
- 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 single-digit number add up to 9?
Elementary Number Sense/About Numbers
Middle School Number Sense/About Numbers
Index of Selected Answers to Common Questions
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