Ta có : a x b x ab = bbb

⇒a x ab = bbb : b

\(\Rightarrow\)a x ab = 111

Ta có :111 = 1 x 111

hoặc : 111= 37 x 3

Mà ab là số có 2 chữ số ⇒a x ab = 3 x 37

Vậy a =3 ; b= 7

a,  Cho hỗn hợp muối ăn có lẫn cát vào nước. Muối ăn tan , cát không tan được ,chìm xuống đáy. Dùng dụng cụ vớt cát ra khỏi hỗn hợp. Ta thu được cát nguyên chất. Sau đó đem hỗn hợp nước muối đun nóng, nước bay hơi còn lại muối ăn. Ta thu được muối ăn nguyên chất.

b. Cho hỗn hợp muối ăn có lẫn dầu hỏa vào nước.  Muối ăn tan trong nước còn dầu nhẹ hơn nên nổi lên mặt nước. Ta dùng dụng cụ vớt dầu ra khỏi hỗn hợp. Thu được dầu hỏa . Tiếp đó, ta đun nóng hỗn hợp nước muối. Nước bay hơi còn lại muối. Ta thu được muối ăn.

 c, Cho hỗn hợp dầu hỏa có lẫn nước vào bình chiết. Dầu hỏa nhẹ hơn nên sẽ nổi lên. Ta mở van để nước chảy ra đến hết, ta khóa van lại. Thu được dầu hỏa và nước

d, Cho hỗn hợp đường và cát vào nước. Dùng dụng cụ khuấy đến khi đường tan. Cát không tan được lắng xuống đáy, dùng dụng cụ vớt ra. Thu được cát. Đun nóng hỗn hợp nước đường, nước bốc hơi còn đường lắng lại. Thu được đường

Tìm tập giá trị, GTLN, GTNN của hàm số sau

\(y=4cos^2\left(\dfrac{x}{2}-\dfrac{\pi}{12}\right)-7\)

Với \(x\varepsilon\left[0;\pi\right]\)

1. Aren't I

2. Will you

3. Will you

4. Will he

5. Isn't ( I think + mệnh đề lấy mệnh đề đề cho đuôi)

6. Needn't they ( must đầu thì đuôi thành needn't )

7. Shall we

8. Isn't it

9. Are they 

10. Isn't it

11. Can't they

12. Did they

13. Did it

14. Aren't I 

15. Wouldn't he

5, It’s very kind ……..you to help me.

A. of                            B. to                C. with                        D. for

6, A free …….. is guaranteed to every citizen.

A. educated                B. education    C. educating    D. educational

7, AIDS is a newly-discovered and very …………………disease.

A. danger                    B. dangerous   C. endangered D. dangerously

8, Please ………your cigarette. I’m allergic to smoke.

A. put aside                 B. put off        C. put  up        D. put out

9, Let’s have a drink,………..?

A. shall we                  B. will we        C. shall you     D. do we

10, They didn’t go on a picnic ……………the weather was awful.

A. so                            B. although     C. because       D. because of

11, Do you know the lady………..son is standing over there?.

A. who                                    B. whom         C. which          D. whose

12, I believe you because I know you are …………

A. true                         B. truth            C. truthful       D. truly

13, Water ……… at 100 degrees Celsius.

A. boiling                    B. boil             C. is boiling     D. boils

14, Laziness is normally the cause of ……….

A. poor                        B. poverty       C. richness       D. success

I.change these sentences into passive

1. Some body clean the house every day

=> The house is cleaned everyday.

2.how do people learn language?

=> How is language learned?

3. John will collect me at the airport

=> I will be collected at the airport by John.

4.mr.Robinson teaches us how to speak english properly

=> We are taught how to speak English properly by Mr.Robinson.

5.your techer must sign this form

=> This form must be singed by your teacher.

6.people play football all over the world

=> Football is played all over the world.

7.our form teacher will hold a class discussion next monday

=> A class discussion will be held by our form teacher next monday.

8.will you invite her to your birthday party

=> Will she be invited to your birthday party?

9. We can't wear jeans at work

=> Jeans can't be worn at work.

10.do thay speak french and english in Canada?

=> Are French and English spoken in Canada?

11.they separated the rice from the husk

=> The rice was seperated from the husk.

112.the boys made a fire by their camp

=> A fire was made by their camp by the boys.

13.they build this house more than on hundred years ago

=> This house was built more than one hundred years ago.

=>Every year millions of tons of rice are exported

15.VietNamese people celebrate theri Lunar New year around January of February

=> The Lunar New Year is celebrated by Vietnamese people around January of February.

16.After Tet holiday VietNamese people usually plant trees in theri neighborhood

=> After Tet holiday, trees are usually planted in their neighborhood.

17.how many festivals do you clerabate in your community?

=> How many festivals are celebrated in your community?

18.how many motorbikes does Viet Nam import a year?

=> How many motorbikes are imported by Vietnam a year?

19. The publisher his book in 1996?

=> His book was published in 1996

20.they repaired our desk during the weekend

=> Our desk was repaired during the weekend.

Tìm tập giá trị, GTLN, GTNN của hàm số sau 

\(y=4cos^2\left(\dfrac{\pi}{2}-\dfrac{\pi}{12}\right)-7\)  Với \(x\varepsilon\left[0;\pi\right]\)