Casting Out Elevens is a slightly slower but more accurate way to sanity check your work. It is a great way to catch most errors including digit reversals (transposing two digits).
Casting Out Elevens can be used when adding numbers of any size.
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Find the digit sum for each number being added.
Add together each digit sum.
Find the digit sum for the addition problems answer.
The addition problems answer is probably correct if the digit sums found in Step 3 and Step 4 are the same.
Casting Out Elevens can also be used for checking your work when adding multiple numbers together.
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