The title of the second volume of the fourth grade diary is "I Learn Chinese"

At noon today, I was doing my math summer homework. As I was writing and writing, I unfortunately encountered a difficult question. I thought about it for a long time and couldn't figure out the reason. The question is like this: There is a cuboid, and the area of ​​the front and the top is 209 square centimeters. And the length, width, and height are all prime numbers. Find its volume. I saw it and thought: This question is really difficult! What is known is only the product of two surface areas, and the volume must also know the length, width, and height, but it does not give any hint at all. How to get this! Wednesday, February 23rd was overcast today. After I went to school to register and returned home, I wrapped up my book cover and started calculating my expenses for this semester. The first is tuition. Tuition fee is 410 yuan, plus 20 yuan for drinking water, ***430 yuan. Next, the fee for the Olympic Mathematics School is 180 yuan, and it is estimated that there is also a transportation fee of 20 yuan, which is 200 yuan. There is also money for exercise books: 2 copies of "Lectures and Lessons" are 21.5 yuan; 1 copy of "English Exercises" is 9.9 yuan; 2 copies of "Examination Papers" are 15.9 yuan; and 3 copies of "Jiangsu Exam Papers" are 21 yuan. 21.5+9.9+15.9+13+21=81.3 (yuan). Study fee: 432081.3=711.3 (yuan). Living expenses: I will drink about 5 cartons of milk this semester, 5×30=150 (yuan). Each meal costs about 2 to 3 yuan. Calculating it at 2.5 yuan, 2.5×3×30×5=1125 (yuan). "What else is there?" I bit my pencil and said to myself, "And your school supplies." Hey, my mother is back. Yes, there are also school supplies. School supplies: a pencil case 8 yuan, a pencil case 3 yuan (very cheap, clearance item), six pencils 3 yuan, an eraser 0.5 yuan, two triangle rulers 1 yuan, two mechanical pencils 5 yuan, 8 +3+0.5+1+5=20.5 (yuan). Total expenditure: 711.3+151125+20.5=2006.8 (yuan). Wow, I didn’t expect that I, who usually don’t spend much money, would actually ask my parents to spend 2,006.8 yuan on me this semester. It seems that I need to save money! Weather on Saturday, September 3, 2005: Cloudy He Jiahong Our New Mathematics Teacher A golden September, the new semester began, and I was lucky enough to meet a new mathematics teacher-Yang Zheng. When you hear this name, don't think she is a man. In fact, she is a female teacher. Tall, with big eyes, he looks like a middle school student. The first lesson she taught was: multiplication and division. When she analyzed mathematical problems, she not only drew pictures, but also cited real life examples, over and over again, until we completely understood and nodded to her. Teacher Yang taught so well. The first class left me with endless aftertaste. Weather on Saturday, September 17, 2005: Cloudy and rainy He Jiahong Why do we like to tell small stories in class? Yesterday, Teacher Yang asked us to discuss why some students like to tell small stories in class? I think the reason for this is not unique. I remember one time in a foreign teacher class, a classmate sitting next to me didn’t like English class and couldn’t understand what the American teacher said. So he came to me secretly to tell small stories. Because I couldn't stand the temptation of his Disney topic, I started "discussing" with him. Later I criticized it to the teacher. I think: speaking small words in class not only affects my own learning, but also affects the learning of others. We must get rid of these bad habits. Sunday, September 25, 2005 Weather: Rain Ho Chia-hung Weighing Shoes Today, one of the math homework questions was to weigh a pair of shoes. So, I went to my mother to ask for a "scale". Mom said she didn't have a "scale." What? However, as the saying goes: "Nothing is difficult in this world." I think there must be a law. So, I used my clever brain and came up with: homemade balance. I cut off the paper of the empty mooncake box piece by piece, took the transparent tape, folded one piece of paper into a right triangle, pasted it and placed it on the countertop. Another piece of paper is used as the left and right plates of the scale, which is balanced on the top of the triangle. Then find some weighted objects at home to use as weights. For example: Mom’s newly bought toothpaste, lipstick and other items include 120g, 40g, 18g and 3g. The exciting shoe weighing activity began. I put the shoe on the left side of the homemade balance, and the "item weight" on the right side. The weight is placed on both sides to balance it. Then add the weights together and the sum is the weight of my shoes. Exactly 86 grams. Hard work pays off! I finally finished my math homework. My mother was full of praise for me when she found out. He also jokingly said to me: "In ancient times, there was a smart Cao Chong who called elephants, and in modern times, there is a smart Honghong who called shoes!" After saying that, everyone burst out laughing. It turns out that there are “scales” everywhere in life! Thursday, September 29, 2005 Weather: Sunny Ho Jiahong’s Happy Math Class Yesterday’s math class, Teacher Yang taught us the section “Going to the Playground”. Because it was about fun projects, the students were very active in asking questions. I am no exception. After thinking about it, I raised my hand and asked this question: "Is 200 yuan enough for 16 people to play all three projects?" After hearing this, Teacher Yang praised me for asking a very difficult question. However, under Teacher Yang’s prompting, I also answered the question for my classmates. I remember a scientist said: "Asking a question is often more difficult than solving a problem." In this math class, we not only asked many questions, but also solved many problems. We are amazing! Sunday, October 2, 2005 Weather: Sunny He Jiahong I am awesome Today, we went to "Happy Valley".

The adult ticket price of Happy Valley is: 140 yuan; half ticket for children. When we were queuing up to buy tickets, my mother asked me to calculate how much it would cost for us to buy tickets. I blurted out: "One pound costs 700 yuan." My mother asked me in surprise how I calculated so quickly. In fact, this is what I think: a half-ticket for 4 children is equivalent to the fare for 2 adults. Plus 3 adults, it is exactly the fare for 5 adults. 140 for 5 is exactly equal to 700 yuan. Mom praised me for being great! Thursday, October 13, 2005 Weather: Clear How many times does Shenzhou 6 orbit the Earth every day? After hearing this, I thought: "So how many times can Shenzhou 6 orbit the earth in one day? So I quickly used my brain to calculate: there are 24 hours in a day, and 1 hour is 60 minutes, that is: 24 times 60 is 1440 minutes in a day. . Then divide 1440 minutes by 90, which equals 16 revolutions. Also, Shenzhou 6 will explore in space for 5 days, which means it will circle the earth 80 times. The weather on Thursday, October 20, 2005: Qing He Jiahong Counting Soybeans Today's math class is a practical activity. We are divided into groups of 8. Then the members of each group work together to estimate how many beans there are in 1 kilogram according to the estimation method introduced in the book. It's not difficult, but you have to be careful to minimize the error. I originally suggested that the group use cups to measure, but the group chose to use their hands to measure. Luo Guangyuan is responsible for catching. Oops! Luo Guangyuan’s little hand is quite big! He caught 1 kilogram of soybeans 30 times in a row. That’s it, I know. There are about 5,400 soybeans out of 1,000. From this practical activity, I was inspired to use these methods to try melon seeds, candies, peanuts, etc. In fact, there seem to be many PS that are closely related to mathematics problems. Just delete it yourself. Just when I was scratching my head in anxiety, a colleague of my mother came. He first taught me to solve it using equations, but I was not very familiar with the equation method, so he taught me again. Another method: first list the numbers, and then eliminate them one by one. We first listed many numbers according to the question requirements, such as: 3, 5, 7, 11 and other prime numbers. Then we started to exclude, and then we found that only one was left. At this time, I thought: one of these two numbers is the front face of the cuboid in the question, the common edge length on the top; the other is the front face of the cuboid, the other edge length besides the above one ( And the length is the sum of prime numbers). So, I started to identify which number each of these two numbers was. Finally, I got the result, which is 374 cubic centimeters. My formula is: 209=11×1919=2+1711×2×. 17=374 (cubic centimeters) Later, I used the knowledge I learned this semester to solve this problem: decomposing prime factors, and the result was exactly the same. After solving this problem, I was happier than anyone else. A truth: Mathematics is full of mysteries, waiting for us to explore. Mathematics Diary February 1st: This evening, I saw a confusing math problem: 37 students want to cross a river, and there is a ferry at the ferry that can only carry 5 people. Empty boat, how many times do they have to use this boat at least to cross the river? Careless people often ignore the "empty boat", that is, they forget to have a punt, so they can only take 4 people at a time. Subtracting one classmate who punted the boat, there are 36 students left. 36 divided by 4 equals 9. The last classmate who worked as a boatman on the other side also went ashore 4 times, so it took at least 9 trips. Mathematics Diary On the evening of March 3rd, I saw a difficult problem in the Olympiad book: There are three times as many apple trees as pear trees in the orchard. Master Wang fertilizes 50 apple trees and 20 pear trees every day. After a few days, the pear trees All the trees were fertilized, but there were still 80 apple trees that were not fertilized. I would like to ask: How many apple trees and pear trees are there in the orchard? I wasn't intimidated by the question; the difficult questions piqued my interest. I think that apple trees are three times as large as pear trees. If both trees are to be fertilized on the same day, Master Wang should fertilize "20×3" apple trees and 20 pear trees every day. In fact, he only fertilized 50 apple trees every day, a difference of 10 trees, and finally a difference of 80 apple trees. From this, we can know that Master Lao Wang has been fertilizing for 8 days. There are 20 pear trees in one day, which means 160 pear trees in 8 days. Based on the first condition, we can know that there are 480 apple trees. This is to use the idea of ​​​​hypothesis to solve problems, so I think the hypothesis method is actually a good way to solve problems. Mathematics Diary April Sunday Today I encountered another mathematical problem and it took a lot of effort to solve it. The question is: There are 30 birds on the two trees. 4 birds fly away from tree B first. At this time, 3 birds fly from tree A to tree B. The birds on the two trees are exactly equal. How many birds were there on each of the two trees? As soon as I read the question, I knew it was a reduction problem, so I solved it using the method of reduction problem. But when I checked, I found it was wrong. I started doing it again more seriously. I think there are the same number after missing 4 trees, so the half is 13 trees, and the restored tree B is 14 trees; the tree A is 16 trees. The formula is: (30-4)÷2=13 (only); 13-3+4=14 (only); 30-14=16 (only). The answer is: 16 trees in tree A and 14 trees in tree B. By solving this problem, I understand that no matter what problem you do, you must be careful, otherwise, even if you master the method of solving the problem, the result will be wrong.

1) Today, our family went to KFC in Longgang to eat a family meal. When we got there, it was always crowded. We finally ordered our food and found a seat to sit down. The food came, a big bucket of set meals. There were 12 chicken drumsticks in it. I thought: How to divide them equally? At this time, I remembered the division 12÷3=4. Each of us had four chicken drumsticks. I later ate one drumstick from my mother and two drumsticks from my aunt. My aunt said, "You can't eat this for free. Let me ask you, how much did you eat? You can eat it again." How many portions do you need to eat them all? "I thought about it and answered: "I ate 7/12, and then I ate them all after eating 5/12." Fortunately, I learned about fractions and could answer the question correctly. ( 2) Today, my mother gave me 10 yuan to buy things in the supermarket. I bought a bunch of firecrackers for 2/10 of the money, four lollipops for 1/10 of the money, and 7 balloons for 2/10 of the money, and finally bought one The comb cost 4/10 of the money, and the comb cost 2/11/12/14/10=9/10. There was only one yuan left and I had to give it back to my mother. After we got home, my mother ate 1/4 of the lollipop, my father ate 1/4 of the lollipop, and I ate 1/4 of the lollipop. There was still one left, which I gave to brother Xiaoqiang next door. eat. (Author: Sean Ling) (3) Last week, we learned about fractions. Fractions have numerators, denominators and fraction lines, for example: 1/3, 3 is the denominator, 1 is the numerator, and the horizontal line in the middle is the fraction line. Fractions are used in many places in life. For example, a book has thirty pages, and each page is 1/30 of a book. Fractions can also be used to add and subtract! For example: one-half plus one-half equals two-half, which is 1. Why is this happening? If a pie is divided into two equal portions, each portion will be 1/2 of the pie. If the two portions are put together, there will be two 1/2 portions, which is exactly one pie. When adding and subtracting fractions, if the denominators are the same, just add the numerators regardless of the denominators. The numerator and denominator of 2/2 are the same, which is 1. I also learned to compare the sizes of fractions. The teacher taught us the following formula: the numerator is the same as the denominator, the fraction with the larger denominator is smaller, and the fraction with the smaller denominator is larger; the denominator is the same as the numerator, the fraction with the larger numerator is larger, and the fraction with the smaller numerator is smaller. The teacher also reminded us that when writing fractions, we usually write the fraction line first, which means the average score, then the denominator, and finally the numerator. Mathematics Diary Weather on Sunday, February: Sunny Mood: Happy Today, our whole school went on an autumn outing. I bought There are a lot of snacks. The snacks I brought this time were eaten by XXX, myself and several classmates. I ate 3/4 of 2 packs of Xizhilang fruit jelly, I drank all the Sprite, 1/5 of a stick of Yida gum, and 1/2 of a bucket of Pringles potato chips with tomato flavor. We ate 4 candies from a pack of Shanghaojia Ice Lemon Hard Candies.

I’m so happy today!