1.Gọi n là  số ngày chị Mai làm theo kế hoạch 
---> Số dụng cụ làm theo kế hoạch là 20n 
Theo đề ra ta có 20n = (n - 2)25 - 10
=>20n=25n-50-10
=>20n=25n-60
=>5n=60
=>n=12
=>số ngày chị Mai làm theo kế hoạch là 12 
mà mỗi ngày chị phải làm 20 dụng cụ 
 Vậy số dụng cụ chị Mai làm theo kế hoạch là:20*12=240 (dụng cụ)

1 she told me that she didn't chocolate

2 she said she wouldn't see me the following day

4 she told me she had visited her parents at the weekend

1. She told me she didn’t chocolate.

2. She said she wouldn’t see me the next day.

3. She said she was living in Paris for a few months.

4. She told me she had visited her parents at the weekend.

5. She said she hadn’t eaten sushi before.

6. She said she hadn’t travelled by underground before she came to London.

7. She said they would help if they could.

8. She told me she would do the washing-up later.

9. She said she could read when she was three.

10. She said she had been sleeping when Julie called”.

Human beings have gained much specific advancement recently. There are a series of inventions that have brought human conveniences in a modern life. Television sets as a good example that certainly influences on our life in communication and entertainment. However, TV also causes some bad effects of time-consuming and health problems.In the first place, television helps people in the ways of communicating to each other and entertaining their life. Thanks to the appearance TV, people can keep up-to-date with the world. What our life will be if we do not have a TV at home. Because TV is a cheap and available tool to provide us daily information. Also, watching TV is a valuable kind of entertainment that helps people relax after working hard or suffering from a busy life. Last but not least, TV has changed husband's behavior in connecting to each other.Beside of good advantages of TV, watching TV may cause some disorders in health and working time as well. Some people spend long hours in front of a TV set, they may neglect then work or duty in taking care of their family members. And young people may work less effectively and addicted to watching TV lead to passiveness and laziness.In conclusion, everything has two sides and TV is optional. It is obvious that TV benefits our life in making people become friendly and close. I totally agree that TV is a great invention and we have to be aware of its good points by using it suitably.

Human beings have gained much specific advancement recently. There are a series of inventions that have brought human conveniences in a modern life. Television sets as a good example that certainly influences on our life in communication and entertainment. However, TV also causes some bad effects of time-consuming and health problems.

In the first place, television helps people in the ways of communicating to each other and entertaining their life. Thanks to the appearance TV, people can keep up-to-date with the world. What our life will be if we do not have a TV at home. Because TV is a cheap and available tool to provide us daily information. Also, watching TV is a valuable kind of entertainment that helps
people relax after working hard or suffering from a busy life. Last but not least, TV has changed husband's behavior in connecting to each other.

Beside of good advantages of TV, watching TV may cause some disorders in health and working time as well. Some people spend long hours in front of a TV set, they may neglect then work or duty in taking care of their family members. And young people may work less effectively and addicted to watching TV lead to passiveness and laziness.

In conclusion, everything has two sides and TV is optional. It is obvious that TV benefits our life in making people become friendly and close. I totally agree that TV is a great invention and we have to be aware of its good points by using it suitably.

ADCT: \(\frac{U_1}{N_1}=\frac{U_2}{N_2}\Rightarrow N_1=U_1\cdot\frac{N_2}{U_2}=200\cdot\frac{110}{100}=220\)(VÒNG)

1. They carried letters by hand over hundreds of kilometers.

2. It cost just one penny.

3. They delivered letters several times a day.

4. They are arranged in the same way as the typewriter.

5. It appeared in the 1870s.

6. Because the talking was perhaps easier than the walking.

7. It was sent in 1992.

8. We send over a billion text messages around the world every day.

* Câu cuối phải là đoạn sau chứ Q ?

1. How did people deliver letters in Ancient Egypt?

=>  people deliver letters in Ancient Egypt  by hand over hundreds of kilometers. 

2. How much did the first stamp cost?

=>The first stamp cost just one penny.

3. How often did they deliver letters in the 1840s?

people delivered the post several times a day.

4. How are the letters arranged on a modern computer keyboard?

the letters are still in the same place on the modern computer keyboard!

5. When did the first fax machine appear?

=> The first fax machine appeared at around the same time (1875)

6. Why was it difficult to walk with the first walkie-talkies?

=> because  the first walkie-talkies weighed around 13.5 kilos

7. When was the first text message?

=> the first text message was sent in 1992

8. How many e-mails do we send every day?

Today we send an incredible thirty-six billion e-mails.

1.there are for people

2.they are message

1. There are four people in the photos.

2. They are using the phone

3. No, they shouldn't because it is bad for their eyes.

Dễ thấy \(0< a,b,c< \frac{3}{2}\)

Thật vậy nếu g/s ngược lại tồn tại 1 số >= 3/2 và g/s đó là a

\(\Rightarrow a\ge b+c\) mâu thuẫn với BĐT tam giác nên ta có điều như trên

Ta có: \(\left(\frac{3}{2}-a\right)+\left(\frac{3}{2}-b\right)+\left(\frac{3}{2}-c\right)\ge3\sqrt[3]{\left(\frac{3}{2}-a\right)\left(\frac{3}{2}-b\right)\left(\frac{3}{2}-c\right)}\)

\(\Leftrightarrow\frac{9}{2}-\left(a+b+c\right)\ge3\sqrt[3]{\left(\frac{3}{2}-a\right)\left(\frac{3}{2}-b\right)\left(\frac{3}{2}-c\right)}\)

\(\Leftrightarrow\frac{1}{2}\ge\sqrt[3]{\left(\frac{3}{2}-a\right)\left(\frac{3}{2}-b\right)\left(\frac{3}{2}-c\right)}\)

\(\Leftrightarrow\frac{1}{8}\ge\left(\frac{3}{2}-a\right)\left(\frac{3}{2}-b\right)\left(\frac{3}{2}-c\right)\)

\(\Leftrightarrow\frac{1}{8}\ge\left(\frac{9}{4}-\frac{3}{2}a-\frac{3}{2}b+ab\right)\left(\frac{3}{2}-c\right)\)

\(\Leftrightarrow\frac{1}{8}\ge\frac{27}{8}-\frac{9}{4}\left(a+b+c\right)+\frac{3}{2}\left(ab+bc+ca\right)-abc\)

\(\Leftrightarrow\frac{1}{8}\ge\frac{27}{8}-\frac{27}{4}+\frac{3}{2}\left(ab+bc+ca\right)-abc\)

\(\Leftrightarrow\frac{3}{2}\left(ab+bc+ca\right)-abc\le\frac{7}{2}\)

\(\Leftrightarrow6\left(ab+bc+ca\right)-4abc\le14\)

\(\Leftrightarrow4abc\ge6\left(ab+bc+ca\right)-14\)

\(\Leftrightarrow3a^2+3b^2+3c^2+4abc\ge3\left(a+b+c\right)^2-14\)

\(\Leftrightarrow3a^2+3b^2+3c^2+4abc\ge13\)

Dấu "=" xảy ra khi: a = b = c = 1

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