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 multiplying numbers of any size.
Example
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Step 1
Find the digit sum for each number being multiplied.
732 digit sum is 6
214 digit sum is 5
Step 2
Multiply each digit sum together.
6 x 5 = 30
Step 3
Find the digit sum of the answer in Step 2
30 digit sum is 8
Step 4
Find the digit sum for the multiplication problems answer.
156648 digit sum is 8
Step 5
The multiplication problems answer is probably correct if the digit sums found in Step 3 and Step 4 are the same.
8 = 8 so 156648 is probably correct.