27 tuổi

Khi đi học, độ tuổi nghĩa vụ quân sự được hoãn đến 27 tuổi

a) 3 2/7 - 2/5 + 5/7 - 3/5

= 3 + 2/7 - (2/5 + 3/5) + 5/7

= 3 + (2/7 + 5/7) - 1

= 3 + 1 - 1

= 3

b) 5 4/7 - 4/9 + 1 3/7 - 5/9

= 5 + 4/7 - 4/9 + 1 + 3/7 - 5/9

= (5 + 1) + (4/7 + 3/7) - (4/9 + 5/9)

= 6 + 1 - 1

= 6

a) \(3\dfrac{2}{7}-\dfrac{2}{5}+\dfrac{5}{7}-\dfrac{3}{5}\)

\(=\left(\dfrac{23}{7}+\dfrac{5}{7}\right)-\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)

\(=4-1\)

\(=3\)

b) \(5\dfrac{4}{7}-\dfrac{4}{9}+1\dfrac{3}{7}-\dfrac{5}{9}\)

\(=\left(\dfrac{32}{7}+\dfrac{10}{7}\right)-\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=6-1\)

\(=5\)

a) \(3\dfrac{2}{7}-\dfrac{2}{5}+\dfrac{5}{7}-\dfrac{3}{5}\)

\(=\left(\dfrac{23}{7}+\dfrac{5}{7}\right)-\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)

\(=4-1\)

\(=3\)

b) \(5\dfrac{4}{7}-\dfrac{4}{9}+1\dfrac{3}{7}-\dfrac{5}{9}\)

\(=\left(\dfrac{39}{7}+\dfrac{10}{7}\right)-\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=7-1\)

\(=6\)

28D

29C

30C

31B

1. ∅

2. a

3. ∅

4. the

5. an

6. the/∅

7. ∅

8. ∅

9. the

10. ∅

1 0

2 a

3 0

4 the

5 an

6 the

7 0

8 0

9 0

10 0

AOB=60 

BOD và AOC = 120 

\(n_{O_2}=\dfrac{1,6}{32}=0,05\left(mol\right)=>n_A=0,05\left(mol\right)\)

=> \(M_A=\dfrac{3}{0,05}=60\left(g/mol\right)\)

=> D