3. if the difference is divisible by 9,
the error is probably either a transposition or a transplacement, and the search can be narrowed down to number where these errors might have been made.
a transporition occurs when 79 is written for 97,318 for 813, and so on.
A transplacement, or slide, occurs when the digits of the number are moved to the left or right, as when 6328.00 dollar is written as 632.80 dollar or 63.28 dollar.