Today, we had an unforgettable math class. The bell rang and the math teacher strode into the classroom. When the teacher announced the content of our lesson "subtraction within 10 thousand", several "naughty boys" chattered and proudly showed off their well-planned plans. Teacher Cao didn't seem to hear, but still smiled and wrote on the blackboard. Suddenly, as soon as the teacher turned around, several subtraction methods learned in grade two appeared on the blackboard, such as' 97-79 =' 82-28 ='. Several "naughty boys" scrambled to tell the result. At this time, the teacher said, "You can also give me a few of this type. Let's see who can calculate faster." As a result, several "naughty bags" were dumbfounded. The teacher did 12, and we only did 4. "God! ..... "Several" naughty boys "scratched their heads, showing a look of dissatisfaction and surprise. See, Teacher Cao said earnestly: "Sometimes seemingly simple questions actually contain a very' beautiful' mystery. Pragmatic and impetuous people often only see the surface! " ……。 "

After listening to Teacher Cao's explanation, several naughty boys showed envy and novelty. "Ah, so that's it! Like' 97-79 =' and' 82-28 =', the number before and after the one-digit exchange can be subtracted from the number on the tenth digit. Subtract the number of one digit from the number of ten digits and multiply it by 9 to get the result of this subtraction, that is, 97-79=(9-7)×9=2×9= 18. It's amazing, it's amazing. " Several "hooligans" shouted. Next, several "naughty" "little faces" quietly retired, and everyone and the teacher cooperated very tacitly throughout the class. We were still intoxicated until the bell rang, and it seemed that we didn't want to leave the classroom. This lesson has been deeply imprinted in our hearts.

Any seemingly simple problem can't be ignored, sometimes there is a deep truth in it.