Add the digits of the first factors that you multiplied. For example, if you multiplied 506 times 437, add 5, 0 and 6 to get 11. If the number has more than one digit, add the digits until you arrive at a single digit. In this case, you would add 1 and 1 to get 2.
Repeat the process from Step 1 for the second factor. In this case, you would add 4, 3 and 7 to get 14. Then you would add the 1 and the 4 to get 5.
Multiply your answers from the first two steps and reduce the answer to a single digit by adding the digits together. In this example, you would multiply 2 and 5 to get 10. Since 1 plus zero is 1, this is your final answer for this stage of the process.
Add the digits of the product that you originally answered and reduce to a single digit. For example, if you obtained the answer 221,122 from multiplying 506 times 437, then you would add 2, 2, 1, 1, 2 and 2 to get 10. Then add the digits from your result together until you get a single digit, as you did in Step 3. In this case, 1 plus zero equals 1. If your answer is the same as the answer you found in step three, then your multiplication is correct.