Doesn't really work.... If you have to multiply say, 27 and 92.... It would be 100-27 plus 100- 92, which is still 73 and 8. Then you're stuck with multiplying 73 and 8 in your head. Barely easier.
So I am going to try to simplify it.
100-97=3 and 100-96=4 If you add 3+4 you get 7 and 100-7 =93 which is the first two digits, while instead of adding it again they multiply 3 times 4 giving you 12 which is the last two digits.
100-97=3 and 100-96=4 If you add 3+4 you get 7 and 100-7 =93 which is the first two digits, while instead of adding it again they multiply 3 times 4 giving you 12 which is the last two digits.