When selecting a Base number, prefer a number that is near the multiplier and multiplicand as well as it should be easy to multiply with (prefer round numbers).
This method uses the concept (B + a) (B + b) = [(B + a) + b] + ab or [(B + b) + a] + ab, where ‘(B + a)’ and ‘(B + b)’ are numbers near a Base number ‘B’ and ‘a’ and ‘b’ are the respective differences.
Whenever the number is more than the Base number, the difference is written as positive (+ve).
Whenever the number is less than Base Number, the difference is written as negative (-ve).
When both numbers are either less or more than Base Number, you add the product of differences.
When one number is more than Base number and another less than Base number, you subtract the product of differences.