36                

ab+ba

= 10a+b+10b+a

= 11a+11b

= 11(a+b) chia hết cho 11

=> ab+ba chia hết cho 11

ta có : 16^x < 128^4

suy ra:2^4x < (2^7)^4

2^4x < 2^28

4x <28

x=(0,1,2,3,4,5,6)

I Find and correct the mistakes

1. There are two benches in my room

2. Mr Hien doesn't live in a house in a country.

3. The Browns is traveling to Ho Chi Minh City in train

4. There isn't a trees to the left of Lan's house

Nhận xét: 
a/ 2 - 1 = 1; 3 - 2 = 1; 4 - 3 = 1; 5 - 4 = 1; 6 - 5 = 1 
b/ Nếu gọi số cần tìm là A thì A + 1 chia hết cho 2, 3, 4, 5, 6 
Phân tích các số : 4 = 2 x 2 
6 = 2 x 3 
Vậy A + 1 = 2 x 3 x 2 x 5 = 60 
A = 60 - 1 = 59 
Vậy số tự nhiên bé nhất chia cho 2 dư 1, chia 3 dư 2, chia 4 dư 3, chia 5 dư 4, chia 6 dư 5 là 59. 

Nhà trường không tổ chức thi thì chịu rồi!

Write an informal e-mail to a friend telling him/her about your weekend.

Hi (tên người bạn),
This weekend, I don´t have to work and I use to work my weekends. It could be fantastic but I have a exam of english. Also I have a very bad exam because my grandmother and cousin were in the hospital. This Fryday, I improve my english for diferents ways as internet or books. My problem is that I´m not creative for writing part. If I have a e-mail for a friend, I don´t think ideas about a free weekend. It´s better for my that I talk about my real situation. After my exam of english I will have other exam more important for me because it´s for my perfect job with children in public education. I´m sorry that I can´t see you but I promise to see you on summer.
Regards,

(thay bằng tên người viết)

Dear Alice,
I haven't talked to you for a long time. How are you doing now? I'm free now so I'm writing this letter to tell you about my free time.
I usually surfing the Internet on my free time. I have plenty of favorite websites and I also write lots of emails. Generally speaking, I see the internet as a good thing. In addition, I enjoy watching movies. I like watching comedy and cartoon because it's make me feel funny and relaxed. Finally, what I like to do in my free time is listening to music. I prefer pop music most. However, I also enjoy listening to rock music and sometimes classic music, it depends on my mood.
What about you? What do you do in your free time? Write me soon.
Best wishes,
Vi.

Bạn nên cho một chủ đề cụ thể

987=9.100+8.10+7.1=9.10²+8.10+7.10⁰

2564=2.1000+5.100+6.10+4.1=2.10³+5.10²+6.10+4.10⁰

abcde=a.10000+b.1000+c.100+d.10+e.1=a.10⁴+b.10³+c.10²+d.10+e.10⁰