At noon today, I was doing my math summer homework. I wrote and wrote, but unfortunately I met a very difficult problem. I've thought about it for a long time, and I can't figure out why. The problem is this: there is a cuboid, the product of the front and the upper two areas is 209 square centimeters, and its length, width and height are prime numbers. Find its volume.
I saw it and thought: this question is really difficult! Only knowing the product of two surface areas, the volume must also know the length, width and height, but there is no hint at all. How does this start?
Just as I scratched my head, a colleague of my mother came for a long time. He taught me to use the idea of equation to solve it first, but I am not very familiar with this method of equation. So, he taught me another way: list the numbers first, and then exclude them one by one. First, we listed a lot of numbers according to the requirements of the topic, such as: 3, 5, 7, 1 1, and then we began to exclude them, and then we found that only1and 19 were left. At this time, I thought: one of these two numbers is the length of the common side of the front of the cuboid in the question; One is the front of the cuboid, and the other is the division of the previous one.
Sum of side lengths (all lengths 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 =11919 = 2+11× 2×17 = 374 (cubic centimeter).
Later, I checked this problem with what I learned this semester: prime factor decomposition, and the results are exactly the same.
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.
2. The fifth grade textbook math diary 500 words.
On Sunday, my mother bought me a fashionable sportswear and a pair of Nike shoes in the mall. When I got home, my father asked, "How much did you buy these clothes, pants and shoes?" I immediately came up with an idea to play a trick on my father, because I knew that my father sometimes didn't speak as fast as me. So I stamped the price tag and said, "I'll call you!" " If you can't figure it out, I'll let you buy me a better suit of clothes and shoes. "Dad said," Then have a try. " "The price of clothes is twice that of 500, minus 600 plus 100, and then the sum of 2 is the price of clothes. Pants are three times 700 minus 1900, and shoes are three times 400 minus 4 plus 200. How much did it cost? " Dad's head suddenly got bigger, so he said, "What is this? Addition, subtraction, multiplication and division. I can't figure it out. " "Well, buy me new clothes!" "No, I haven't answered the answer yet." "Well, you listen up. (500×2-600+ 100)÷2=250 yuan, 700×3- 1900=200 yuan, 400×3÷4+200=500 yuan total * * * 250+200+5000. Dad said, "Wow, that's what it is. All right, I'll give you new clothes. "Yes, I won this round, Dad.
It turns out that many things in life can be solved by mathematics. I will continue to discover mathematics in my life and learn more calculation methods.
3. The fifth grade textbook math diary 500 words.
Today, I followed my mother to the market to buy food. Mom said, "I will test you today. Will you buy a dish you like?" My mother gave me 20 yuan to watch my performance. "Make sure the task is completed." I said confidently. So, I walked and watched, and came to the vegetable area. At this moment, I saw an aunt selling white and tender fresh mushrooms. I think: the leftovers at home can be cooked with mushrooms. So, I asked the aunt who sells vegetables: "Aunt, how much is a catty of mushrooms?" Aunt smiled and said to me, "Little friend, this mushroom costs 7 yuan a catty. How much catty do you want?" "Aunt, I only need to buy half a catty." I think: 7 divided by 2 equals 3.5 yuan, 20 minus 3.5 equals 16.5 yuan. After thinking about it, I gave my aunt a note of money from 20 yuan, reminding her that she still needs to find me 16.5 yuan. I went to the meat department again and saw an uncle selling meat, so I asked, "Uncle, how much is a catty of meat?" "10 yuan a catty." "Then I'll buy a catty." I thought: 16.5 minus 10 equals 6.5 yuan. I handed the 10 yuan in 6.5 yuan to my uncle. When I came out of the market, my mother saw that I had both meat and vegetables and 6.5 yuan in my hand. She smiled and said to me, "Learn to buy vegetables!
"Through this test, I feel that there are many mysteries of mathematics hidden in our lives, and the ability to learn mathematics is really important. And don't be proud. You should study hard and master more math skills in order to apply what you have learned and solve the problems around you.
4. Five-grade math diary 500 words.
We studied equations this semester. I learned that equations are equations, but they are not necessarily equations. Through learning, I know that both sides add or subtract the same number at the same time, and the result is still an equation, which is the essence of the equation; Multiply or divide both sides by a number that is not equal to 0, and the result is still an equation, which is also the nature of the equation. I learned two methods when solving equations. One is to use the properties of the equation, such as:10+x =15, which can be considered as:10+x-10 =15-65438. One is to use the relationship between addition, subtraction, multiplication and division, for example: 10+ⅹ= 15 to write ⅹ= 15- 10, and the calculation result is ⅹ=5.
In life, we can use equations to solve practical problems. Once, my aunt's family was decorating a new house, and they wanted to buy some light bulbs. Different rooms bought different light bulbs. My uncle made a list. 40W ordinary bulbs 16, 50W cold reflection directional lighting halogen bulbs (installed in the living room), 30w ordinary bulbs, and1/w energy-saving bulbs (installed in the kitchen and bathroom). These bulbs have different functions and their prices vary greatly. My uncle asked me and grandpa to buy it and gave him 400 yuan. We came to the lamp market, where there are many kinds of light bulbs, and the prices of various brands vary greatly. I really don't know what to buy. Grandpa said to me, "Come and give me a hand. How to buy it? " I said to grandpa, "That must be distributed reasonably." Buy ordinary light bulbs first. We think that the price of a 40W ordinary light bulb is the same as that of a 25W ordinary light bulb, and each 4 yuan needs 46×4= 184 yuan. The price of energy-saving 1 10W light bulb is 12 yuan, and it needs 12×6=72 yuan. In this way, 4X+256=400, then 4X= 144 and X=36. According to this calculation, we have a goal to buy tungsten halogen lamps with similar prices and enough money.
5. Five-grade math diary 500 words.
At noon, my father came back from work, humming a ditty, and happily stepped into the house. I greeted him and asked, "Dad, what's so happy today?" My father said, "I got a raise this month." I asked, "How much salary do you get now?" Father thought for a moment, smiled and said, "I am higher than my salary." Our monthly salary adds up to 2800, and the monthly salary difference is 100. How much do you think I get a month? " After listening to my father's words, I began to draw line drawings on paper to help me understand:
Through observation and thinking, I quickly worked out the answer and told my father. First of all, mom's salary is as much as dad's, so mom and dad's monthly salary is (2800+ 100)=2900 yuan, and then the total monthly salary is divided into two parts, and 1 part is dad's monthly salary. The formula is: (2800+ 100)÷2= 1450 yuan.
Dad listened and nodded with satisfaction. At this time, my mother, who was cooking, said to me, "Do you have any other methods?" "There are other ways." I'm surprised. I stopped to observe and think curiously. I found that the key to this problem is to find out who is the standard. Different standards have different methods. So, I have a second method: taking mom's salary as the standard, assuming mom and dad's salary is the same, then the sum of their monthly salary is (2800- 100)=2700 yuan, and then divide the sum of monthly salary into two parts on average. 1 part is mom's monthly salary, and finally it is more than mom's 100. The formula is (2800-100) ÷ 2+100 =1450 yuan.
After listening to the second method I introduced, mom and dad both laughed. ...