Để cho ra quặng 66% thì cần trộn tỷ lệ quặng 75% : quặng 50% là 82/75 : 1 hay 82/75 : 75/75.
Như vậy để có 25 tấn quặng 66% thì cần:
Quặng 75%
(82 x 25) : (82 + 75)= 2075/157 tấn
Quặng 50%
(75 x25) :(82+75)= 1875/157 tấn

GIVE THE CORRECT FORM OR TENSE OF THE VERBS IN BRACKETS.

1.      It (take) ………………. him 2 hours every day to practise speaking English when he was a student.

2.       When you (start) ……………… school?

3. Tom isn't here. He just (go) ………………… out for a few minutes.

4. We (have) ……………… an English test next week.

5. We (waste) ……………… too much power at the moment.

6. Please don't make so much noise. I (study) ………………………..

7. They suggest (take) ……………… a bus instead of using private car to save energy.

8. You (meet) …………… Nam last Sunday? Oh, no. I (not see) ………………. him for a long time.

9. My parents (go) ……………… out 10 minutes ago. They will be back soon.

10. My brother (work) ………………     for Samsung Corporation since 2009.

CHOOSE THE BEST ANSWER AMONG A, B, C OR D TO COMPLETE THE SENTENCES.

1.      There is a _____ between the North and the South.

       A. different          B. differ                   C. differently          D. difference

2.      I planned to have a swim this morning but the weather is so _____.

       A. disappointed   B. bored                  C. uninterested      D. disappointing

3.      We learn foreign languages _____ know more about other people and countries.

       A. so that              B. in order to          C. just as                 D. for we

4.      She will be disappointed _____ she gets the job.

       A. but                    B. unless                 C. because              D. if

5.      He was absent from school _____ his illness.

       A. because            B. because of          C. as                         D. for

6.      Jimmy is not _____ to go to school alone.

       A. young enough                                  B. old enough         C. enough old    D. enough young

7.      - “Would you like a glass of green tea?”                            - “ _____ ”

       A. Yes, let's          B. No, thanks          C. No, let's not       D. No, I don't

8.      You had a headache yesterday, _____?

       A. hadn't you        B. do you                 C. didn’t you          D. did you

9.      When we looked at the baby last night, he _____.

       A. sleep                 B. slept                    C. sleeping              D. was sleeping

10. Let's not go out today, _____?

       A. shall we           B. shan't we            C. will you              D. won't you

Cho tam giác ABC vuông tại A (AB < AC), đường cao AH, nội tiếp đường tròn (O). M là điểm chính giữa cung AC. Tia BM cắt AC tại E cắt tiếp tuyến tại C của (O) tại F. OM cắt AC tại K.

a)Chứng minh tứ giác AHOK nội tiếp.

b)Chứng minh tam giác CEF cân

c)Chứng minh OM tiếp xúc với đường tròn ngoại tiếp tam giác AOB