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 subtracting numbers of any size.
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Find the digit sum for each number being subtracted.
Subtract the two digit sums.
Find the digit sum for the subtraction problems answer.
The subtraction problems answer is probably correct if the digit sums found in Step 2 and Step 3 are the same.