六八 五十七

My wife, a professor with Ph.D., was reading a paper.  Talked to herself "六八 五十七".  After hearing that, I thought to myself that it is impossible to have the product of two even numbers to be an odd number.  Then she talked to herself again "七八 五十六".

Realizing that she was citing multiplication table, I asked her "How can you add one more 8 to a number but result in a number one smaller?"