hình như là A

(x+1)+(2x+3)+(3x+5)+...+(100x+199)=30200

 =(x+2x+3x+..........+100x)+(1+3+5+......+199)=4950

=x.(1+2+3+.........+100)+(1+3+5+.......+199)=4950

=>5050x+10000=30200

=>5050x=30200-4950

=>5050x=25250

=>x=25250:5050

=>x=5

Câu 21: A

Câu 22: C

Câu 23: C

Câu 24: B

Câu 25: A

hello teacher, my nam i.... (giới thiệu bản thân) 

here, i will talk about my topic: talk about green activities and their benefits to the environment. The first is to plant trees. Trees help absorb Co2 and release gas 02, helping to cool the atmosphere. In addition, it provides shade, fruit and can store a large amount of watter. second, is waste recycling. It helps to treat wastes that pollute the environment, some plastics can even be processed for use. the third, choose green transport like carpooling, bus or bicycle. talking the bus helps reduce a part of emissions into the air, contributing to reducing the greenhouse effect. Cycling can both avoid tracffic jams in the city, improve your health,etc.... Thank you very much. 

activities: plant trees, recycle trash, clean the citiy

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Quãng đường AB dài: \(3.5\cdot60=210\left(km\right)\)

Thời gian người đi xe máy đi hết quãng đường AB là:

\(\dfrac{210}{40}=\dfrac{21}{4}\left(h\right)\)

Quãng đường AB dài là:

\(60\times3,5=210\left(km\right)\)

Người đi xe máy đi hết quãng đường trong:

\(210\div40=5,25\left(giờ\right)\)

Đáp số: 5,25 giờ

Cảm ơn các bạn nhiều nha.

Quãng đường AB dài là: 60x3,5=210km

Người đi xe máy đi với vận tốc 40km/h trong : 210 : 40 = \(\dfrac{21}{4}\left(h\right)\) = 5,25h = 5h 15 phút

Quãng đường dài : 3,5 x 60 = 210 ( km)

người đi xe máy đi hết : 210 : 40 = 5,25 ( giờ )

Quãng đường AB dài :

  3,5.60=210(km)

Một người đi xe máy hết số thời gian là:

 210 : 40= 5,25(h)

   Đáp số : 5,25h 

1. By the time, I decided to go on a diet, I had put on ten kilos.

2. They waxed the car after they had washed it.

3. Before Lisa sat on the sofa to watch TV, she had made a sandwich

4. As soon as we packed our suitcases, we left for the airport

5. When the lecture started, I entered the lecture hall

6. This is the first time I have tasted Chinese food

7. He has never read a science-fiction book before

8. Như câu 2

9. While Mark was parking his car, he noticed the wing-mirror was broken

10. Ad Judy was walking down the street, she saw an accident

11. I'm sorry I can't take to you now as I'm about to work

12. The Council intends to close the old swimming pool

13. They are planning to have a big wedding in the summer

14. The economy is on the point of collapsing

15. My grandfather is about to go far, far far far far far far far away : (

16. You are due to arrive at 7.30 in the evening

D

B

D

B

4D

5B

L R A

Lỗi ạ

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