Math diary 1 In the sixth grade of primary school, at noon, I had nothing to do after lunch, so I picked up an excellent student question bank. Open the chapter on negative numbers, read the previous explanation, and turn to the exercise section to do exercises. I watched the exercises first. Although there is a lot of content, it is very simple. I thought, "Hi! This is also called "top student question bank". It's so simple that I can do it with my eyes closed. "
So, I began to do the questions, fill in the blanks and judge the questions. I made two pages in a short time. Speaking of application problems, I thought it would be more difficult, so I read it carefully. This is not difficult at all. After two or three strokes, only one application problem was written. I scribbled the question. It's simple. No, it's accelerated. What are these "+15" and "-15" for? I'll think about it. I just can't answer the question. I read the question again, but I still can't. At this time, I thought of a formula I saw in a book, which seemed to be just right for this problem. I quickly turned out all the reference books on mathematics I bought, and read and reread them. Why not? I clearly saw this formula in the book, how could I not find it?
Facts are facts, so I flipped through the back answer: 200 ÷ (35+15)+200 ÷ (35-15) =14 hours. Why divide 200 by 35? At this time, in the question of travel, I picked up the book "General Review of Primary School Graduation" and turned to the page about travel. There is a formula that makes me suddenly realize that it is like this: distance divided by speed equals time, and these plus fifteen and minus fifteen are addition and subtraction, not symbols.
Math problems really need to be understood carefully! It seems simple, but in fact it contains complexity. Whatever you do, be serious and don't underestimate it.
The sixth-grade teacher of math diary No.2 Primary School often said: There is mathematics everywhere in life. In life, at this time, many ordinary little things can be turned into funny and thought-provoking math problems. The math problems we often do are to solve problems in life. No, I found an interesting math problem while eating hamburgers:
It takes three minutes for three people to eat three hamburgers, and how many minutes for nine people to eat nine hamburgers?
My mother often takes my brother and me to eat hamburgers. I only know how to eat. At this time, I never thought I could turn it into a math problem to do. It's really funny to encounter this problem. At first I thought: It takes three minutes for three people to eat three hamburgers. It's not a minute for one person to eat one hamburger, and it's not nine minutes for nine people to eat nine hamburgers. . I was so excited to think about it that I quickly told my mother the answer. But my mother frowned and said, "Son, think about it. Think about how we and my brother eat hamburgers. Use your head more! " "I was shocked, and the pride just disappeared. I calmed down and thought about it. It suddenly occurred to me that it takes three minutes for three people to eat three hamburgers. In fact, it takes three minutes for one person to eat one hamburger and three minutes for nine people to eat nine hamburgers. I didn't tell my mother the answer at once, but I thought it over and over again several times. At this time, I thought there should be no problem before telling my mother the answer. Mother nodded and smiled and praised me as a clever boy. She added, "Mathematics comes from life. As long as you observe carefully, you will get something, just like eating hamburgers. "
Look, a little thing in life can also become a funny math problem. Mathematics is really everywhere! Let's love math and learn it well!
Math diary, Grade Three, Grade Six This morning, my mother suggested going to Zijingshan Park. I am very happy. I jumped three feet and wanted to be a superman. I dragged my mother to fly to Zijingshan Park!
Dad took us to Zijingshan Park and wouldn't let me get off without asking you. Dad said to us mysteriously, "Only when you answer the question correctly can you get off the bus." Dad proudly said to us, "Suppose it's100km from home to Zijingshan Park. Take a taxi from 6 yuan, walk 10 km, stay in 5 yuan every 10 km, and wait for the traffic lights for the longest time. My eyes rolled and I had a brainwave. Multiplying100-10 = 9090 ÷10 = 99 by 5=45 (yuan) 45+6=5 1 (yuan) 1.25 times 5 is about 6.3.
As soon as I entered the door, I was surprised. Many people gathered in one place, as if in a meeting. One person shouted and won the grand prize by answering math problems for free. How much has it increased from 1 to 9999? When I heard it was a math problem, I was overjoyed and in high spirits. Mom adds them one by one, and forgets them at 238. As soon as I thought the answer was right, I racked my brains and finally solved the problem.
(1+9999) times 4999+5000.
= 10000 times 4999+5000
=49990000+5000
=49995000
I immediately told the answer and my thoughts. He said excitedly, "This boy got it right!" Everyone opened my eyes with envy, and my mother said, "Great Yang Jinsong. "
There is mathematics everywhere in life. As long as you pay attention to it, you can find it!
Last time we visited our old friend "percentage", this time we continue to discuss the percentage of "old friends".
Last time, only the "first wisdom gate" of percentage application (1) was discussed, that is, the application of finding the phase difference first and then dividing it by the unit "1"; After that, let's visit the "Second Door of Wisdom". Do you have the courage to accompany me to explore? Come if you have it!
As soon as I entered, I saw a problem that must be understood. For example, the price of an induction cooker in Sunshine Supermarket is 320 yuan, which is cheaper than the original price in 80 yuan. The price of induction cooker has dropped by several percent. Let's explore slowly. Teacher Zhang told us: "This line is a kind of flashback in percentage application. When encountering these problems, we must first complete key sentences. " For example, we add "the price of 20 yuan" before "80 yuan is cheaper than the original price", so that we can explore it better. We can calculate the unit "1" first, the original price is 320+80=400 yuan, and we know the difference (80). Then we divide the first 80 by 400, which equals 20%. We got the key to the second small door, and we continued to open the second small door, only to see a formula "Find a company to know the difference" 65438+. We explored the percentage of "the second door of wisdom" and I learned a lot. Now let's compare.
The first is that we don't know the difference, and the second is that we know the difference; The first is that we know the unit "1", and the second is that we don't know the unit "1". The first one is easy for us to do. We just need to find the difference before and divide it by the unit "1". The second one is more difficult, but we just need to complete the sentence, then find the unit "1" and divide it by the unit "1".
At noon, I'm in math diary Grade 5, Grade 6, and I'm doing winter vacation homework in Mathematics. Unfortunately, I met a very difficult problem. I thought about it for a long time and didn't come up with one, so later. The problem is this: there is a cuboid, the product of the front and the upper area is 209 square centimeters, and the length, width and height are prime numbers. Find its volume.
I saw it and thought: this question is really difficult! We only know the area of two faces, and the volume must also know the length, width and height, but there is no hint at all. How does this start?
Just as I was scratching my head, my mother came. My mother taught me to solve the equation first, but I am not very familiar with this method of equation. So, my mother taught me another method: first list the numbers and then exclude them one by one. First of all, we listed many numbers according to the requirements of the topic, such as: 3, 5, 7, 1 1 and so on. And then began to exclude, and then found that only 1 1 and 19. At this time, I thought: one of these two numbers is the common side length of the front and top of the cuboid in the problem; One is the front of a cuboid, and the top is divided by the sum of the lengths of other sides (both are prime numbers). So, I began to tell which number these two numbers were.
The final result is 374 cubic centimeters. My formula is: 209 =119 = 2+171× 2×17 = 374 (cubic centimeter).
I am happier than anyone to solve this problem. I also understand the truth that mathematics is full of mysteries, waiting for us to explore.
Math diary Last Saturday, in the sixth grade of primary school, my mother and I went to our hometown in the countryside. Along the way, I saw farmers' uncles harvesting sweet potatoes. They smile at the farmer's uncle like fat dolls. My mother told me, "Now is the sweet potato harvest season", and then she said to herself, "Today's sweet potatoes are rich again." I said, "What's the use of collecting so many sweet potatoes?" Mom said: "Sweet potato can play a great role! Can be made into sweet potato skin, sweet potato powder, sweet potato strips ... "
Knowing that I learned the percentage, my mother asked me: 50 Jin of sweet potato can squeeze out 5 Jin of sweet potato powder. What is the flour yield of these sweet potatoes? If grandma squeezes 500 Jin of sweet potatoes this year, how much sweet potato powder can grandma collect? I calculated:
550× 100%=0. 1× 100%= 10%
500× 10%=50 (kg)
After I finished the calculation, I said to my mother, "The output of sweet potato powder is 10%, and grandma can receive 50 Jin of sweet potato powder this year." I asked my mother curiously, "What does Grandma do with so much sweet potato powder?" Grandma said, "Our special snack in Pingtan-salty rice is indispensable. Our family of three needs 0.4 Jin of sweet potato flour for a salty rice meal. Then grandma gave us 10 Jin, so how many times can we cook salty rice? " I calculated: 10 ÷ 0.4 = 25 (times)
I said to my mother, "I can do it 25 times." Mom said: "Eat salty rice twice a month on average, is it enough for one year?" I said, "I can't finish it yet. I can add another meal during the Chinese New Year. " Mom said, "You are really good. In fact, it can also be made into vermicelli soup, vermicelli and vermicelli knot. "
Math diary, Grade 7 Today, we met our "old friend" again. Let's review the percentage of "old friends" first, because "review old friends and learn new ones"! In the past, we mainly studied the application of two percentages. The first is to find the percentage of one number to another: what percentage is one number divided by another? The second is to find out how much one number is more (less) than another. Today we will learn to find out how much one number is more than another.
We slowly explored the mystery with the amiable teacher Zhang, but found nothing. Teacher Zhang met us, taught us some little truths, and also used teacher Zhang's old method to "analyze the topic". We analyzed the topic, for example, "There is 45 cubic centimeters of water in the box. After it forms ice, the volume of ice is about 50 cubic centimeters. The volume of ice has increased by several percent compared with the original volume of water. " According to teacher Zhang's method, we frame the volume of ice, the original volume and percentage of water in the question with rectangles, draw triangles under "ratio" and "about increase", and write 50 cubic centimeters under "volume of ice" in the title. In this way, we groped slowly, and we understood the solution to this problem. The solution to this problem is to find the phase difference first, and then divide it by the unit "1". In these foundations, we should pay attention to finding the correct unit "1". Find it right, and you are half right about this question!
The percentage of "old friends" is back. Let's discuss this "old friend" again.