This question is a number game, because the money owed contains ten dollars, which should be 980=970+ 10. Or 1000=970+20+ 10. This question is only ten dollars short, which is easy to confuse people, but it can be changed: I spent ten dollars on shoes and paid my parents ten dollars respectively, which is the same as everyone owes 490, but there is still 970 left. What if 970+980= wow, 1950! ! Make a lot of money ... the calculation result is meaningless ...