\ r \ n \ r \ One day, my mother and I went shopping. Mom went into the supermarket to buy things and let me stand at the place where I paid. I have nothing to do, just watch the assistant aunt collect money. After reading it, I suddenly found that the money collected by the assistant aunt was 1 yuan, 2 yuan, 5 yuan, 10 yuan, 20 yuan and 50 yuan. I feel very strange: Why isn't RMB from 3 yuan, 4 yuan, 6 yuan, 7 yuan, 8 yuan, 9 yuan or 30 yuan, 40 yuan or 60 yuan? I ran to ask my mother, and my mother encouraged me to say, "Think hard and calculate well. Mom believes that you can find out the reason. " I calmed down and thought it over. After a while, I jumped up happily: "I know, because as long as there is 1 yuan, 2 yuan, 5 yuan, 3 yuan, 4 yuan, 6 yuan, 7 yuan, 8 yuan and 9 yuan can be formed at will, as long as there is 10, 20 yuan, 50 yuan, 30 yuan, 40 yuan and 60 yuan, they can also be formed ... Why should it be 2 yuan and 5 yuan?" I said, "It is not convenient to use only 1 yuan to form a larger number." Now my mother shows a satisfied smile and praises me for observing more and thinking more. I am really more comfortable than eating my favorite ice cream. \ r \ n \ r \ Here, I also want to tell other children: In fact, there are math problems everywhere in life. As long as you pay more attention to observation and thinking, you will find many unexpected discoveries. Try it if you don't believe me!