On Sunday, I went to my aunt's stationery store to buy school supplies. It happened that my aunt had something to do, so let me watch the shop for a while. Soon, an uncle came, and he said that he would test me before he could tell me what to buy. He said, "Zhang Dan bought a pencil and an exercise book and spent 0.60 yuan. Exercise books cost twice as much as pencils. What is the unit price of pencils and exercise books? I thought about it: exercise books and pencils are three times * * *, and the price of pencils can be calculated with 0.60÷3, so can the price of exercise books. I said the unit price of pencil is 0.20 yuan, and the unit price of exercise book is 0.40 yuan. My uncle praised me for my cleverness: "It's good to analyze the topic carefully! "You each exercise book 0.6 yuan, each composition book 0.9 yuan. I want to buy 10 copies and give you 8. 1 yuan. Keep the change. How many exercise books and composition books should you give me? I thought about it and said, "We assume that all the books in 10 are composition books, and you need 10×0.9 = 9 yuan, and you actually paid 8. 1 yuan, that is, 9-8. 1 = 0.9 yuan, and the actual composition book is 0.9-0.6 = I figured it out. My uncle praised me for being smart, and I was flattered. Later, my uncle bought some stationery, and I was still immersed in joy when I checked out. As a result, I miscalculated the money I didn't find it, but my uncle said to me, "You, if you praise me, you will get carried away." I misread the decimal point of the money I should have paid, and as a result I underpaid 15.3 yuan. "I'm sorry, the decimal point moved one place to the left, which is 10 times smaller than the original price, with a difference of 9 times. As long as 15.3÷9= 1.7 yuan, it's just 10 times smaller, so it's 1.7× 10 = 65438. Aunt bought some more stationery and left.

Today, I have really gained a lot. Mathematics in my life is really everywhere. Mathematics is really advanced. I will work harder and strive for a higher level!