How to use it
- Choose a base such as 100.
- Write each number as base plus or minus an offset.
- Use expansion or cross-adjustment and add the offset product.
See it in action
97×96 = (100−3)(100−4) = 10000−700+12 = 9312.
How to verify it
Estimate 100×100 = 10000; a result around 9300 fits.
Common mistake
Track signs carefully when one number is above the base and the other is below.