Mathematics is everywhere in life!

I did something at home today, that is, I measured a one-dollar coin.

The tools are: a set of rulers, a one-dollar coin and a colored pen.

First, draw the diameter of a dollar coin with crayons. Its diameter is 2.5 cm. Calculate the circumference of a circle, 2.5 times 3. 14 equals 7.85 cm. If you know the radius of a circle, you have to multiply 3. 14 by 2 to calculate the circumference of the circle.

I also know that the line segment connecting the center of the circle and any point on the circle is called diameter, which is generally represented by the letter R. The line segment passing through the center of the circle with both ends at the center is called radius, which is generally represented by the letter D. The center of the circle determines the position of the circle, and the radius determines the size of the circle.

I had nothing to do at home today, so I found an old four-wheel drive wheel. I began to measure its circumference. It's hard to find points, so I borrowed several methods from a class. Because the wheel is installed here, it is difficult to measure. Finally, I drew a circle on the paper according to the size of the wheel.

Measure the diameter. 3,14× 2,5 = 7,85 (cm).

This is really an interesting measurement!

Part II: Clever solution to geometric problems.

At noon today, I was doing my math summer homework. Writing, unfortunately, I have a problem. I thought about it for a long time, but I couldn't figure out a way. The question is this:

There is a cuboid, the product of the front and the upper two areas 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! 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 was scratching my head, a colleague of my mother came. 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 =119 = 2+171× 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.

The third article: interesting twenty-four points

On Sunday, Yang Wen and I played 2 1 point. The rules of the game are simple: everyone draws four cards respectively, and then uses these calculation methods of "+,-,×, ⊙", and the final number must be 24.

The game started, and we each drew four cards. Alas! How come my cards are so bad! Listen, four people are all trump cards. At this moment, I only heard Yang Wen say, "I can do it. You see, 5+5= 10, 10×2=20, 20+4=24. " I lost the first round. But I am not discouraged, because there are still opportunities in the future, and I must seize them and strive for them. I drew four more cards "6, 5, 8, 3". I was so excited that I blurted out immediately: "6-5= 1, 8× 3 = 24,24 ÷1= 24. Now 1 is even with 1. "

Yang Wen said, "Anyway, I will definitely beat you in the next round." The third round arrived, and I drew four more cards "10, 9, 6, 10". I was dumbfounded at first sight. Suddenly, Yang Wen shouted: "6× 4 = 24,24+1-1= 24. 2 1 I won. " I watched him smug and helpless.

Although I lost the game, I think 24 o'clock is really interesting and math is really wonderful. I must study math well in the future and use the mixed operation of "+,-,×, ⊙" flexibly. In the next 2 1 point game, I must skillfully use it and become a master.

Article 4: Sweet potatoes have many uses.

On Saturday, my mother and I went to our hometown in the country. Along the way, I saw farmers' uncles harvesting sweet potatoes. They smile at the farmer's uncle like fat dolls. My mother told me, "It's sweet potato harvest season", and then she said to herself, "Today, 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 had 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:

5/50× 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. "

Chapter 5: How tall is this big tree?

On Saturday morning, my mother and sister went to Liangshan Park to play, and a big tree caught my eye. Mother asked, "Huanhuan, can you reach the height of this tree?" "Ok, use a bamboo pole as high as it, and then measure the length of that bamboo pole." Mother retorted, "Where did you get such a long bamboo pole?" "I ... I ..." I scratched my head. Suddenly I caught a glimpse of the shadow of the tree on the ground, and an idea flashed through my mind: by the way, didn't the teacher just teach the knowledge of proportion? I said excitedly, "Sister! Lend it to you! " My sister is puzzled: "How do you ask?" "In the same place, at the same time, the length of the shadow is proportional to the length of the object. Measure your height first, then the length of your shadow, calculate the ratio of your height to your shadow, then measure the shadow length of this big tree and calculate the height of this big tree. " I am proud to say.

Because I usually like small production, I always take a tape measure with me. I first measured my sister's height 1.56m, and then measured the length of her shadow by 0.52m. Their ratio is: 1.56: 0.52 = 3: 1. I measured the shadow length of this big tree as 1. 1m, and then calculated the height: 65438. My mother and sister looked at me with thumbs up. I thought happily: Mathematics is really useful!