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. Looking at 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 think it's very strange: But why isn't there RMB of 60 yuan from 3 yuan, 4 yuan, 6 yuan, 7 yuan, 8 yuan, 9 yuan or 30 yuan, 40 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 see, 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 combined at will, and as long as there is1yuan, 20 yuan and 50 yuan, they can also be combined into 30 yuan, 40 yuan and 60 yuan."

My mother nodded straight and asked me another question: "Isn't 1 yuan enough if it's just for random combination?" Why 2 yuan and 5 yuan? "I said," it is not convenient to use 1 yuan to form a larger number. "Now my mother showed a satisfied smile and praised me for observing more and thinking more. I am really more comfortable than eating my favorite ice cream.

Here, I also want to tell other children: in fact, there are math problems everywhere in life. However, as long as you pay more attention to observation and think more, you will find many unexpected discoveries. Try it if you don't believe me!

2. Grade five math diary 400 words.

After several turns by car, I finally came to Beijing, the capital of our country. There are many tall buildings, clean streets and crowded people in Beijing. I asked my mother before that the hotel we stayed in was called Gone with the Wind Home. What a special name. I really want to stay in a hotel right away. Dad decided to take us to the subway station. Wow, that's great. Let's buy tickets. Four dollars for three people. how much is it? I calculated in my mind that 3×4 is equal to 12 yuan, and my father gave me 20. I calculated how much I was looking for, and 20- 12 equals 8. Looking for 8 yuan, dad smiled and didn't go to school for nothing! The hotel finally arrived, and my mother checked in at the front desk. The sister at the front desk asked: Hello, do you have a reservation? How many nights are you going to stay? We pay 308 yuan per night. Mom said: 308 a night, stay for 5 nights, you calculate. So I started to calculate 308×5= 1540 seriously. Wow, it's so expensive! Mom also said that we booked it online and returned it in 80 yuan overnight. How much do you have to pay? I asked my mother, what does it mean to go back to 80? My mother told me that the price of staying for one night can be: negative 80 yuan. Mom, I get it. (308-80)×5= 1 140 My sister at the front desk gave me a thumbs-up sign. Great, little beauty. I didn't expect math to be very common in life!

3. Grade five math diary 400 words.

Today, I read a question in the encyclopedia of solving problems of Olympic mathematics in primary schools. A rectangle is divided into four different triangles. The area of the green triangle accounts for 15% of the rectangular area, and the area of the yellow triangle is 2 1 cm2. Q: How many square centimeters is the area of a rectangle? Seeing this topic, I was very confused and thought: if you only tell the area occupied by one and the area of another triangle, how can you find it? My mother sitting in the chair took a look, smiled at me and said, "Hum, she said she is so advanced that she can't even know this problem, hehe."

I know my mother used the goad method, in order to irritate my competitive spirit and let me finish this problem. In order to make my mother think that her provocation was successful, I crustily skin of head did it, but I couldn't figure it out. But I'm not discouraged. I persisted and finally succeeded.

According to the figure, we can find that two red triangles account for half of the rectangle, a yellow triangle and a green triangle account for half of the rectangle, and the green triangle accounts for 15% of the rectangle area, so the yellow triangle accounts for 50%- 15% = 35%, and our division ratio is 2135% =

It turned out to be so simple, thanks to my mother's provocation!

4. Grade five math diary 400 words.

Today, my grandparents and I went shopping in Zhangdian Commodity City. There are so many people here! I thought: What if I get lost? Suddenly I saw a lot of people in a circle, as if watching something. I squeezed in and saw that it was a floor plan of a small commodity city. Grandma came to me and asked me gently, "Chen Feng, do you know which side of the elevator is the toy area?" "North". I blurted out, "Do you know which direction the toy section and stationery section are?" This time I thought for a while before answering: "Northwest." "It's very kind of Chen Fengzhen. How about grandma rewarding you with a toy? " "Well, well!" I jumped up with joy, and then we excitedly ran to the toy area in the northwest corner ... At night, I looked out of the window at the dark sky and asked my mother, "My mother, what did you say, it was so dark at night that those picnickers got lost?" My mother pointed to a star and said, "Well, look, that's the Big Dipper. It is in the north, so those people will not find the wrong direction as long as they see the Big Dipper. " "Oh, so that's it!" I breathed a sigh of relief and fell asleep.

5. Grade five math diary 400 words.

Let me tell you a little secret. I, a smart and capable girl, have a very annoying problem, which is carelessness. My Chinese score is not bad, but my math is not so good. Don't think that I can't solve math problems, in fact! I was so careless. There was a math exam, and I couldn't wait to do it as soon as the test paper was issued. The second problem is calculation. Let me see, haha! It's simple. After correcting the paper, the teacher called me to the office and said to me angrily and humorously, "Look, how can 132+4 be equal to 128?" How can it be less and less? " Another time, I copied 34× 2 = 68 in the draft into 34× 3 = 68, and sometimes I missed the question.

The most interesting thing is that once I answered a question: 433× 2 = 856, the teacher kindly said to me, "You are too careless. Don't think that this problem is nothing, but it is actually very harmful. If I grow up to be a scientist, what will happen if the calculation error is one millimeter when the missile is launched? If you become a doctor and the patient's index finger is cut off, what will happen if you cut off all his ten fingers! "

After listening to the teacher's words, I regret and feel sad, and my face is burning red. Yes, "if a small hole is not mended, a big hole will suffer." I decided to turn over a new leaf and get rid of my carelessness.