Giúp mình bài này với ạ ! mình cảm ơn trước!
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Mỗi giờ làm chung, hai bạn làm được:
1:7= 1/7 (công việc)
Lượng việc Tâm phải làm 1 mình là:
1 - 5 x 1/7 = 2/7 (công việc)
Mỗi giờ Tâm làm 1 mình được:
2/7 : 6= 1/21 (công việc)
Nếu làm 1 mình, để hoàn thành công việc Tâm mất:
1 : 1/21= 21(giờ)
1 giờ làm 1 mình thì Thành làm được:
1/7 - 1/21= 2/21(công việc)
Nếu làm 1 mình, để hoàn thành công việc Thành mất:
1: 2/21= 10,5(giờ)
a.
2 should
3 must
4 must / have to
5 don't have to
6 don't have to
7 should
8 mustn't
9 shouldn't
10 must / should
b.
2. You should have a rest.
3. Everyone will have to speak.
4. v
5. I had to stay in bed.
6. You mustn't park
7. v
8. People shouldn't answer
XIV.
1. Her sister is more beautiful than her
2. English exercises is more difficult than Literature exercises
3. My new class is bigger tham my old class
4. Phi is more handsome than anybody in the class
5. Loan is taller than anyone in the family
IV.
3. French is not as difficult as English
4. That house is bigger than this house
5. A new house is more expensive than an old house
6. Yesterday is not as hot as today
7. My sister is taller than me
8. Girls are not as strong as boys
X.
1. Lesson 1 is not as long as Lesson 2
2. Ha Noi is smaller than HCM City
3. Old English is not as difficult as new French
4. Quang is not as thin as Quan
5. Your computer is more expensive than my computer
XI.
3. Minh is thinner than Hoang
4. Driving a motorbike is not as difficult as driving a car
XII.
1. Boys are stronger than girls
2. I am more intelligent than my sister
3. A new house is more expensive than an old house
4. English is more difficult than French
5. That river is longer than this river
6. New films are more interesting than old films
XIII.
3. Quan is the most intelligent student in my school
4. HCM City is the biggest city in VN
1 A
2 B
3 B
4 A
5 D
6 C
7 D
8 C
9 A
10 D
11 C
12 B
13 D
14 B
15 C
16 B
17 A
18 D
19 B
20 C
1:
Đặt AB=x; CM=y
Theo đề, ta có: 4x-4y=28 và x^2-y^2=119
=>x-y=7 và x^2-y^2=119
=>x=y+7 và y^2+14y+49-y^2=119
=>y=5
=>S=5^2=25cm2
a. Tổng có 52 hạt
\(\rightarrow p_X+e_X+n_X=52\)
\(\Leftrightarrow2p_X+n_X=52\left(1\right)\)
Số hạt mang điện nhiều hơn số hạt không mang điện là 16 hạt
\(\rightarrow p_X+e_X-n_X=16\)
\(\Leftrightarrow2p_X-n_X=16\left(2\right)\)
Từ (1) và (2) \(\rightarrow p_X=e_X=17\) và \(n_X=18\)
b. \(M_X=p_X+n_X=17.1,013+18.1,013=35,455đvC\)
c. \(m_X=35,455.1,9926.10^{-23}=7,065.10^{-22}g\)