gọi khối lượng 2 thanh kim loại là x (kg)

ta có: A = 9x; B = x

thể tích khối A là: \(\dfrac{9x}{2700}=\dfrac{x}{300}\)

thể tích khối B là: \(\dfrac{x}{7800}\)

tỉ số thể tích giữa khối A và khối B là: 

\(\dfrac{\dfrac{x}{300}}{\dfrac{x}{7800}}=\dfrac{x}{300}\cdot\dfrac{7800}{x}=\dfrac{7800}{300}=26\)

BÀI 4: gọi d là quãng đường AB 

thời gian dự định để đi từ A đến B là: \(t=\dfrac{d}{50}\)

thời gian đi 2/3 quãng đường là: \(t'=\dfrac{\dfrac{2}{3}d}{50}=\dfrac{2d}{150}=\dfrac{d}{75}\)

thời gian đi 1/3 quãng đường là: \(t''=\dfrac{\dfrac{d}{3}}{40}=\dfrac{d}{120}\)

tổng thời gian thực tế đi từ A đến B là: \(t'+t''=\dfrac{d}{75}+\dfrac{d}{120}\)

theo đề, thời gian thực tế đi chậm hơn 30p nên ta có: 

\(\dfrac{d}{75}+\dfrac{d}{120}=\dfrac{d}{50}+0,5\\ \dfrac{4d}{300}+\dfrac{2,5d}{300}=\dfrac{6d}{300}+0,5\\ \dfrac{6,5d}{300}=\dfrac{6d}{300}+0,5\\ 6,5d=6d+150\\ 6,5d-6d=150\\ 0,5d=150\\ d=300\)

vậy quãng đường AB dài 300km

mình làm lại câu h xíu

\(\dfrac{3}{8}\cdot x-\dfrac{1}{2}=\dfrac{3}{4}\\ \dfrac{3}{8}\cdot x=\dfrac{5}{4}\\ x=\dfrac{5}{4}:\dfrac{3}{8}=\dfrac{5}{4}\cdot\dfrac{8}{3}\\ x=\dfrac{10}{3}\)

\(\left(2\dfrac{2}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\right):\left(-\dfrac{3}{17}\right)\\ =\left(\dfrac{32}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\right)\cdot\left(-\dfrac{17}{3}\right)\\ =\dfrac{32}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\cdot\dfrac{-17}{3}\\ =\left(\dfrac{32}{15}\cdot\dfrac{3}{32}\right)\cdot\left(\dfrac{9}{17}\cdot\dfrac{-17}{3}\right)\\ =\dfrac{1}{5}\cdot\left(-3\right)=-\dfrac{3}{5}\)

đối với danh từ không xác định thì không nên đưa vào trong câu bị động

1 If you didn’t live so far away, we would visit you more often
2 If the book were not so expensive, I would buy it
3 If we could afford it, we would go out more often
4 If we had some money, we could go on the trip
5 If you don’t water these plants, they will die
6 If I didn’t have to work late tomorrow, I would join your party
7 If you don’t study harder, you won’t pass the final exam
8 If we had had more money, we could have bought that house
9 If I were free today, we could go to the beach
10 If the film weren’t so boring, they wouldn’t have to leave the theater now
11 If you don’t pass this exam, you won’t get the scholarship
12 In case it rains on your way home, bring a raincoat with you
13 If you don’t eat less meat, you’ll gain much weight
14 If I were you, I wouldn’t accept his invitation
15 Should you arrive at the office earlier than I do, please turn on the air-conditioner
16 Had he not died so young, he would be a famous musician by now
17 But for the rain, we would have a better crop
18 If I were you, I wouldn’t buy it
19 If he hadn’t had money, he wouldn’t have bought such a big house
20 If you don’t get a visa, you can’t visit the USA
21 As long as you arrive before eleven, I can meet you
22 If Peter didn’t eat so many chips, he wouldn’t be fat
23 If Robert hadn’t started smoking cigarettes, he wouldn’t have gotten a bad cough
24 Unless you like this one, I’ll bring you another
25 Unless she hurries, she’ll be late
26 If it hadn’t been for Jack’s help, I wouldn’t have been able to move this table
27 If it weren’t for Helen, the play would be a flop
28 If I hadn’t had you, I would have given up years ago
29 If she hadn’t had a visa, she couldn’t have come to that country
30 As long as you drive carefully, you can use my car
31 If she were rich, she would travel around the world
32 If you go right now, you will catch a bus
33 Should you see Peter, tell him he should be here at 8:00
34 If you were to find some buried treasure, what would you do
35 But for Paul’s interest, the project would have been abandoned
36 If you happen to find my wallet, could you let me know

🙂🙂

1 There isn't much progress left on the project. Do we need to pick up the pace
2 We learned many interesting facts on our visit to the museum
3 There's not much energy left in my phone. I need to charge it
4 I have many questions about the instructions for this recipe
5 There isn't much room left in the car for more passengers
6 Many people attended the lecture on climate change
7 How much exercise would you like to do today
8 I don't have much free time this weekend
9 There are many delicious desserts at the bakery
10 We didn't get much sleep last night because of the storm
11 There aren't many choices left on the menu. Some items are sold out
12 Would you like much more soup with your lunch
13 Much effort has been put into making this event a success
14 There wasn't much traffic on the highway this morning, so my commute was quick
15 I don't have much experience working in customer service
16 How much luggage are you allowed to check in for your flight
17 There's not much information available online about this topic
18 We don't have much money left in our budget for this vacation
19 There are many beautiful butterflies in the garden this summer
20 I don't have much confidence in my ability to win this competition