a: x=3/4-1/3=9/12-4/12=5/12

b: 1/3x=2/3-5/9=6/9-5/9=1/9

=>x=1/3

c: =>3x=6/5-3/4-7/4=6/5-5/2=12/10-25/10=-13/10

=>x=-13/30

d: =>x+2/5-2/3=5/3

=>x=5/3+2/3-3/5=7/3-3/5=35/15-9/15=26/15

e: =>1/4:x=2/5-3/4=8/20-15/20=-7/20

=>x=-1/4:7/20=-1/4*20/7=-20/28=-5/7

f: =>1/4x-3/4=1/2-25/4=2/4-25/4=-23/4

=>1/4x=-20/4

=>x=-20

21. Tinh told Lien that she might go shopping with her friends

22. Bao said he had to do more grammar exercise

23. The girl said they ought to finish their homework that night

24. The leader of the group said that they would play with their best to win the prize for their school

26. The coach told the players to train harder for the next match

27. Tam's sister told him to  help her to clean the house

28. Hoa's parents said that they would visit her that summer

30. Mary told her friend that she would expect to see him/her the next Wednesday

tách bài ra nha b

3 C
4 B

5 A

6 B

7 A
8 A

9 C

10 D

11 B

12 B

13 A

14 C

15 B

16 A

17 D

18 D

19 C

20 A

21 B

22 B

23 C

24 D

25 B

26 D

27 A

28 D

29 C

30 B

31 C

32 A

33 A

Viết lại câu

12 

Authorities in Ho Chi Minh City suggested that current school break schould be extended by us until the end of March to control the epidemic caused by Covid-19

15 The plumber who has just been had check the pipes in my house is very skillful

16 In spite of the fact that we had invited her to the party, she didn't come

17 Since they didn't have a map, they lost their way

18 I suggest that energy-saving bulbs should be used to reduce the electricity bill

19 We are looking forward to seeing your gook action from your company 

20 Linda congratulated Owen on scoring a wonderful goal

21 She had all the water pipes in her house checked by the plumber yesterday

22 If you go on smoking, you will be seriously sick

23 I suggested all the bag should be collected and taken to the garbage dump

24 If you aren't carefull, you will fall over the rocks

25 If you work too much, you will feel tired

26 If you are careless, you'll break the vase

1 The girls really like rehearsing a play with friends

2 My younger brother prefers reading books to playing outdoor games

3 The harvest time occured earlier  than we had thought

4 Children in the countryside knw about technology less cleary than children in big cities

My younger brother adores watching historical films

Bài 6.

a)Công suất ấm: \(P=\dfrac{A}{t}=\dfrac{900\cdot1000}{10\cdot60}=1500W\)

Dòng điện qua ấm: \(I=\dfrac{P}{U}=\dfrac{1500}{220}=\dfrac{75}{11}A\)

Điện trở dây nung: \(R=\dfrac{U}{I}=\dfrac{220}{\dfrac{75}{11}}=\dfrac{484}{15}\Omega\)

b)Điện năng tiêu thụ trong 1 tháng (30 ngày):

\(T=900\cdot1000\cdot30\cdot3600=9,72\cdot10^{10}J=27000kWh\)

Tiền điện phải trả: \(T=27000\cdot1500=40500\left(k.đồng\right)\)

c)Công suất tiêu thụ thực: 

\(P=UI=\dfrac{U^2}{R}=\dfrac{110^2}{\dfrac{484}{15}}=375W\)

Bài 7.

CTM: \(\left(Đ_1ntR_b\right)//Đ_2\)

\(R_1=\dfrac{U_{Đ1}^2}{P_{Đ1}}=\dfrac{10^2}{2}=50\Omega;I_{Đ1đm}=\dfrac{P_{Đ1}}{U_{Đ1}}=\dfrac{2}{10}=0,2A\)

\(R_2=\dfrac{U^2_{Đ2}}{P_{Đ2}}=\dfrac{12^2}{3}=48\Omega;I_{Đ2đm}=\dfrac{P_{Đ2}}{U_{Đ2}}=\dfrac{3}{12}=0,25A\)

Để đèn 1 sáng bình thường \(\Rightarrow I_b=I_{Đ1đm}=0,2A\)

\(R_{Đ1+b}=\dfrac{12}{0,2}=60\Omega\)

\(R_b=60-R_{Đ1}=60-50=10\Omega\)