Ta có: 1/2=10/20=1.10/20=1/20+1/20+1/20+.....+1/20(10 số 1/20)

Vì các p/s từ 1/11->1/19 đều lớn hơn 1/20 nên Ta có: 1/11+1/12+1/13+....+1/20>1/20+1/20+1/20+.....+1/20(10 số 1/20)                                                            =>   A                                   >1/20+1/20+1/20+.....+1/20(10 số 1/20)

Vì số 18 và 12 đều chia hêt cho 3

Nên kẹo phải là số chia hết cho 3

Vì Giang đưa cho cô bán hàng 2 tờ 100000 và được trả lại 72 000 nên số tiền mua được 18 gói bánh và 12 gói kẹo là

       100 000 x 2 - 72 000 = 128 000 (đồng)

Vì số 128 000 đồng không chia hết cho 3 nên Trang nói " Cô tính sai rồi " OK 

Số số hạng của dãy số là :

(8192-1):1+1=8192 (số)

Tổng của dãy số là :

(8192+1)*8192:2=33558528

Đáp số :33558528

1. She's quite musical, she plays the flute and the piano.

2. He was hopeless when he did the test badly.

3. We started our trip on a beatifull sunny morning

4. I enjoyed the book very much because it was so readable.

5.His geographic knowledge is very poor. He thinks Paris is in Italy

6. Her hair is dark red, not bright red

7. A very old car is usually an unreliable car

8. I'll always remember that journey. It was an unforgettable experience

9. The knife may need sharpened before it is used

10. The city has over million inhabitants

11. The cost of admission to the show is reasonable.

12. My teacher is very knowing about the history of Viet Nam

13. There's too much greed in the word.

14. She thinks that with a little flattery she can persuade her husband to change his mind.

15. He feels a great deal of shame for the awful way he behaved.

16. It's humiliating to be laughed at in public

17. Mr. Smith is a independent person. If he says he will do something, you know that he will do

18Theoretically, there are black hotes in space

19. The results of the first experiments are very promising

20. The sun and the moon are often personalize in poetry

Ta có:

9²⁰=(3²)²⁰=3⁴⁰

27¹³=(3³)¹³=3³⁹

Mà 3³⁹<3⁴⁰

Suy ra: 27¹³ <9²⁰

9^{20  <}< 27¹³

đúng 100%

duyệt