Diary related to learning Unit 12 in the first volume of the fourth grade math book in math diary Middle School.

Summer is almost over, and many businesses have posted billboards to reduce prices, some with a 5.8% discount and some with a 60% discount. X Xtep slogan (plus 19 or 29 yuan). I'll ask, buy a pair of shoes and get one free. If the price is the same, pay the price of a pair of shoes plus 29 yuan. If the price is different, pay a pair of expensive shoes plus 65438+. I see. I quickly called my good friend to buy shoes together. We selected two pairs of RMB 258 and 198 yuan respectively. As soon as the result is worked out, we have to pay 258+ 19 = 277 yuan. If we give a 60% discount, we have to pay (258+ 198)* 0.6 = 273.6 yuan, so a 60% discount is better. We re-selected two pairs of shoes with the price of 208 yuan, so we paid 208+29 = 237 yuan. If we give you a 60% discount, we have to pay 208 * 2 * 0.6 = 249.6 yuan, so it's a good deal to buy one and get one free!

It seems that buying one get one free is not necessarily cheaper than discount, but depends on how to send it and how to discount it.

Knowledge of handling grain

Today, my mother watched Lucky 52 on TV, and there was a question in it. Pupils didn't get the doctor's answer correctly. My mother asked me to do it. The topic is: A monkey carries 0/2 bags of corn every day and eats 7 bags at night. When can this monkey move 500 bags of corn? A: 99 days. Answer B 100 days. Answer C: 10 1 day.

I think: 12-7=5 (bags), that is to say, five bags are moved every day, so 500÷5= 100 (days).

I'm laughing in my heart. Suddenly, I thought: On the last day, if I move without eating, there will be 500 bags. Then, 1 day should be reduced, so it takes 100- 1=99 days. I handed in my "paper" at my mother's place, and her mother said, "Congratulations, you got it right. Wow, I "

go shopping

Today is the weekend. In the afternoon, I went shopping with my grandparents

We walked into the Jeanswest store, and grandma chose three T-shirts from 29 yuan and bought them. Grandma asked me, "How much is this * * *?" Without thinking, I said, "One * * 87 yuan (29×3 is about 90,90-3×1= 87 yuan)."

After grandma bought clothes, we walked out of the clothing store. Grandma said, "It's already half past five. Let's eat rice noodles. " Walking into the rice noodle shop, we bought a bowl of medium rice noodles, two bowls of small portions, one steamed dumpling and two bowls of porridge. Grandma asked me, "How much should I pay?" I said, "One * * 1 7 yuan, because the middle portion is 4.50 yuan, the small portion is 3.50 yuan, the steamed dumpling is 3.50 yuan, and the porridge is1yuan (4.50+3.5× 3+/kloc-0 /× 2 =/kloc-0).

After eating, we went home.

Buy oranges

In life, mathematics is everywhere. For example: buy food! Buy stationery! Measuring cloth, etc. , all need to use mathematics.

This semester, the teacher taught a new knowledge, that is, the multiplication and division of decimals. This knowledge helps me a lot!

Last night, my mother went to buy oranges together. A kilo of oranges is 1.8 yuan. My mother bought 4.5 kilograms and should pay 8. 1 yuan. However, the clerk was careless and didn't know how to calculate, so it became 9 yuan money. Fortunately, I used the knowledge of Protestantism this semester to calculate 1.8/2 = 9 (angle) 1.8x4 = 7.2 (yuan) 9 +7.2 yuan = 8. 1 yuan in my mind, which immediately corrected the clerk's mistake.

In such a small city, my aunt, the shop assistant, not only praised me for my cleverness and ability of decimal multiplication and division, but also praised me for saving 0.9 yuan for her on my way home, and the knowledge I learned can be applied to my life.

Yes! If you don't learn this math well, you will lose not only this 0.9 yuan, but also hundreds, thousands or even hundreds of millions.

When can the snail climb out of the well?

Today, I saw a thinking question in a book:

A snail was trapped in a well15m deep. This snail climbs 1 m every day and falls 30 cm in the middle of the night. When can the snail climb out of the well?

I listed the formula on the draft paper: the snail climbs 65,438+000-30 = 70cm every day, 65,438+00 days, 70× 65,438+00 = 700cm, and 20 days, 70× 20 = 65,438+0400cm, leaving 65,000. It takes 20+ 1=2 1 day for a snail to climb out of the well.

It turns out that there is mathematics everywhere in life!

The weather will get better on Sunday, September 9.

What is mathematics?

Today, I heard grandma tell a story.

This is the true story of the famous Polish mathematician Selma Pinski.

One day, he was ready to move, and his wife took out his luggage and said to him, "I'll call a taxi, and you look after the luggage here, *** 10 box." After a while, my wife came back. He said to her, "Just now you said there were 10 boxes, but I counted only nine." "No, it must be 10." "What are you talking about? I'll count it again, 0.1.2,3. . . . . . "

Oh, I see. Mathematics consists of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.

September 9(th), 2007

Angle understanding

In our life, we can touch things related to mathematics everywhere.

Take the horn as an example. As long as you observe carefully, you can find many things related to horns. For example, the clock we often see, when noon is 12: 30, I find a flat angle on the clock face. If it takes another 10 minutes, an obtuse angle will appear. If it takes another 5 minutes, that is, 12: 45, a right angle will appear. When the pointer moves 15 minutes, that is, 1, an acute angle will appear on the clock face.

I listened to it, and after reading it, my heart was full of joy. I want to learn math well and apply what I have learned to my present life.

The story of decimal point

Although the head of the decimal point is small, I know the decimal point is not small.

For example, 3.80 yuan, without a decimal point, doesn't it become 380 yuan? The gap between 3.80 yuan and 380 yuan is too big! Can't you see how big the decimal point is with such a comparison?

Many students often miss it when writing, so this number is not what you originally wanted to write. So let's not make this big mistake again!

Eat some candy

Today, my mother bought some sugar. I can't wait to eat two fifths first. Then, I took a sip of water and went to do my homework. After finishing the Chinese preview homework and math exercise book, I ate another fifth. Then my mother said, "What sugar is so greedy?" I want some, too. "In this way, we ate four-fifths of the sugar, and my mother asked me," How much sugar is left? " I replied, "Only one fifth of the sugar! "On this day, I expressed the sugar we ate with mathematical knowledge. I am really happy now.