(10a+c) (10b+c) =100a b+/kloc-0 (a+b) c+c× c =100 (ab+c)+c× Give two examples: 42× 62 = 2604 Because 2 times 2 equals 4, the last two digits of the result are 04, and then 4× 6+2 = 26 is the first two digits, which adds up to 2604. Similarly, 25×85=2 125 is because 2× 8+5 = 2 1 is the first two places.