Question

Tính giá trị các biểu thức sau theo cách hợp lí nhất.
a) $\mathrm{A}=\left(\dfrac{2}{7} \cdot \dfrac{1}{4}-\dfrac{1}{3} \cdot \dfrac{2}{7}\right):\left(\dfrac{2}{7} \cdot \dfrac{3}{9}-\dfrac{2}{7} \cdot \dfrac{2}{5}\right)$;
b) $\mathrm{B}=\dfrac{\left(\dfrac{1}{5}-\dfrac{2}{7}\right) \cdot \dfrac{3}{4}-\dfrac{3}{4} \cdot\left(\dfrac{1}{3}-\dfrac{2}{7}\right)}{\dfrac{1}{5} \cdot \dfrac{2}{7}-\dfrac{1}{3} \cdot\left(\dfrac{2}{7}+\dfrac{3}{9}\right)+\dfrac{3}{9} \cdot \dfrac{1}{5}} .$

Answer 1

Answer 2

rêtrt

Answer 3

A= 5/4

B= 63/52

Answer 4

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Answer 5

a) \mathrm{A}=\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]=\left(\dfrac{1}{4}-\dfrac{1}{3}\right):\left(\dfrac{1}{3}-\dfrac{2}{5}\right)=1 \dfrac{1}{4}A=[72​(41​−31​)]:[72​(31​−52​)]=(41​−31​):(31​−52​)=141​.
b) \mathrm{B}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{1}{3}+\dfrac{2}{7}\right)}{\dfrac{1}{5}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)-\dfrac{1}{3}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{1}{3}\right)}{\left(\dfrac{1}{5}-\dfrac{1}{3}\right)\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=1 \dfrac{11}{52}B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+3

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Answer 6

a) \mathrm{A}=\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]=\left(\dfrac{1}{4}-\dfrac{1}{3}\right):\left(\dfrac{1}{3}-\dfrac{2}{5}\right)=1 \dfrac{1}{4}A=[72​(41​−31​)]:[72​(31​−52​)]=(41​−31​):(31​−52​)=141​.
b) \mathrm{B}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{1}{3}+\dfrac{2}{7}\right)}{\dfrac{1}{5}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)-\dfrac{1}{3}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{1}{3}\right)}{\left(\dfrac{1}{5}-\dfrac{1}{3}\right)\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=1 \dfrac{11}{52}B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+

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Answer 7

A =1 1/4
B =1 11/52

Answer 8

\(a,A=\left(\dfrac{2}{7}.\dfrac{1}{4}-\dfrac{1}{3}.\dfrac{2}{7}\right):\left(\dfrac{2}{7}.\dfrac{3}{9}-\dfrac{2}{7}.\dfrac{2}{5}\right)\)

   \(A=\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}.\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]\)

 \(A=\left(\dfrac{2}{7}.\dfrac{-1}{12}\right):\left(\dfrac{5}{15}-\dfrac{6}{15}\right)\)

\(A=\dfrac{-1}{42}:\dfrac{-1}{15}\)

\(A=\dfrac{-1}{42}.\dfrac{15}{-1}\)

\(A=\dfrac{5}{14}\)

Answer 9

\(a,A=\left(\dfrac{2}{7}.\dfrac{1}{4}-\dfrac{1}{3}.\dfrac{2}{7}\right):\left(\dfrac{2}{7}.\dfrac{3}{9}-\dfrac{2}{7}.\dfrac{2}{5}\right)\)

   \(A=\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}.\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]\)

 \(A=\left(\dfrac{2}{7}.\dfrac{-1}{12}\right):\left(\dfrac{5}{15}-\dfrac{6}{15}\right)\)

\(A=\dfrac{-1}{42}:\dfrac{-1}{15}\)

\(A=\dfrac{-1}{42}.\dfrac{15}{-1}\)

\(A=\dfrac{5}{14}\)

Answer 10

a) A = (\(\dfrac{2}{7}.\dfrac{1}{4}-\dfrac{1}{3}.\dfrac{2}{7}\) ) : ( \(\dfrac{2}{7}.\dfrac{3}{9}-\dfrac{2}{7}.\dfrac{2}{5}\) ) = \(\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]\)

                                                               = \(1\dfrac{1}{4}\) 

 

 

Answer 11

\(a,A=(\dfrac{2}{7}.\dfrac{1}{4}-\dfrac{1}{3}.\dfrac{2}{7}):(\dfrac{2}{7}.\dfrac{3}{9}-\dfrac{2}{7}.\dfrac{2}{5})\)

\(=(\dfrac{1}{4}-\dfrac{1}{3}):(\dfrac{1}{3}-\dfrac{2}{5})\)

\(=1\dfrac{1}{4}\)

\(b,B=\dfrac{\dfrac{3}{4}(\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{1}{3}+\dfrac{2}{7})}{\dfrac{1}{5}(\dfrac{2}{7}+\dfrac{1}{3})-\dfrac{1}{3}(\dfrac{2}{7}+\dfrac{1}{3})}\)

\(=\dfrac{\dfrac{3}{4}(\dfrac{1}{5}-\dfrac{1}{3})}{(\dfrac{1}{5}-\dfrac{1}{3})(\dfrac{2}{7}+\dfrac{1}{3})}\)

\(=1\dfrac{11}{52}\)

Answer 12

           

Answer 13

A = ( 2/7 . 1/4 - 1/3 . 2/7 ) : ( 2/7 . 3/9 - 2/7 . 2/5 )

A = 2/7 . [( 1/4 - 1/3 ) : ( 3/9 - 2/5 )]

A = 2/7 . [ -1/12 : -1/15 ]

A = 2/7 . 5/4

A = 5/14

B = ( 1/5 - 2/7 ) . 3/4 - 3/4 . ( 1/3 - 2/7 ) / 1/5 . 2/7 - 1/3 . ( 2/7 + 3/9 ) + 3/9 . 1/5

B = 3/4 - 3/4 / 3/9 + 3/9

B = 0 : 2/3 

B = 0

 

Answer 14

Answer 15

    

Answer 16

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Answer 17

Answer 18

a) A= 5/4

b) B= 63/52

Answer 19

A=15/12

B=63/52

Answer 20

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Answer 21

a,A=[2/7(1/4-1/3)]:[2/7(1/3-2/5)]

=(1/4-1/3):(1/3-2/5)

=6/4

b, B= .3/4(1/5-2/7-1/3+2/7)/1/5(2/7+1/3)-1/3(2/7+1/3)

=3/4(1/5-1/3)/(1/5-1/3)(2/7+1/3)

=63/52

Answer 22

A=(2/7.1/4-1/3.2/7):(2/7.3/9-2/7.2/5)

=2/7.(1/4-1/3):(2/7.(3/9-2/8))

=2/12-4/12):(15/45-18/45)

=-1/12.45/-3=5/4

B=(1/5-2/7).3/4-3/4.(1/3-2/7)

_______________________

1/5.2/7-2/7-1/3+2/7+3/9)=3/4.1/5

=3/4.(1/5-2/7-1/3+2/7)

_________________

1/5-(2/7+3/9)-1/3918/63=21/63)

=3/4.(1/5-1/3)

__________________________

1/5-(18/63+21/63)-1/3(19/63+21/63)

=3/4.(1/5-1/3)

_____________________________

(1/5-1/3)18/63+21/63)

=3/4:39/63=3/4.21/13=63/52

Answer 23

A=5/4

B=63/52

Answer 24

A=9/8 , B=2/4

Answer 25

13 tháng 7 2022 lúc 15:10  

a) \mathrm{A}=\left[\dfrac{2}{7}\left(\dfrac{1}{4}-\dfrac{1}{3}\right)\right]:\left[\dfrac{2}{7}\left(\dfrac{1}{3}-\dfrac{2}{5}\right)\right]=\left(\dfrac{1}{4}-\dfrac{1}{3}\right):\left(\dfrac{1}{3}-\dfrac{2}{5}\right)=1 \dfrac{1}{4}A=[72​(41​−31​)]:[72​(31​−52​)]=(41​−31​):(31​−52​)=141​.
b) \mathrm{B}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{1}{3}+\dfrac{2}{7}\right)}{\dfrac{1}{5}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)-\dfrac{1}{3}\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=\dfrac{\dfrac{3}{4}\left(\dfrac{1}{5}-\dfrac{1}{3}\right)}{\left(\dfrac{1}{5}-\dfrac{1}{3}\right)\left(\dfrac{2}{7}+\dfrac{1}{3}\right)}=1 \dfrac{11}{52}B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+

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Answer 26

a) A = \(\dfrac{5}{4}\)

b) B =\(\dfrac{63}{52}\)

Answer 27

a) A=[27(14−13)]:[27(13−25)]=(14−13):(13−25)=114A=[72​(41​−31​)]:[72​(31​−52​)]=(41​−31​):(31​−52​)=141​.
b) B=34(15−27−13+27)15(27+13)−13(27+13)=34(15−13)(15−13)(27+13)=11152B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+31​)

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Answer 28

a) A=[27(14−13)]:[27(13−25)]=(14−13):(13−25)=114A=[72​(41​−31​)]:[72​(31​−52​)]=(41​−31​):(31​−52​)=141​.
b) B=34(15−27−13+27)15(27+13)−13(27+13)=34(15−13)(15−13)(27+13)=11152B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+31​)

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Answer 29

a) A= \(\dfrac{2}{7}\times(\dfrac{1}{4}-\dfrac{1}{3})\div\dfrac{2}{7}\times(\dfrac{3}{9}-\dfrac{2}{5})\)

    A= \(\dfrac{2}{7}\times\dfrac{7}{12}\div\dfrac{2}{7}\times\dfrac{-1}{15}\)

    A= \(\dfrac{1}{6}\div\dfrac{-2}{105}\)

    A= \(\dfrac{-35}{4}\)

b) B= \(\dfrac{(\dfrac{1}{5}-\dfrac{2}{7})\times\dfrac{3}{4}-\dfrac{3}{4}(\dfrac{1}{3}-\dfrac{2}{7})}{\dfrac{1}{5}\times\dfrac{2}{7}-\dfrac{1}{3}(\dfrac{2}{7}+\dfrac{3}{9})+\dfrac{3}{9}\times\dfrac{1}{5}}\)

     B=\(\dfrac{\dfrac{3}{4}(\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{1}{3}+\dfrac{2}{7})}{\dfrac{1}{5}\times\dfrac{2}{7}-\dfrac{1}{3}\times\dfrac{2}{7}+\dfrac{1}{3}\times\dfrac{3}{9}+\dfrac{3}{9}\times\dfrac{1}{5}}\)

     B= \(\dfrac{\dfrac{3}{4}[(\dfrac{1}{5}-\dfrac{1}{3})-(\dfrac{2}{7}-\dfrac{2}{7})]}{\dfrac{2}{7}(\dfrac{1}{5}-\dfrac{1}{3})+\dfrac{3}{9}(\dfrac{1}{3}-\dfrac{1}{5})}\)

     B=\(\dfrac{\dfrac{3}{4}(-\dfrac{2}{15}+\dfrac{1}{7})}{\dfrac{2}{7}\times(\dfrac{-2}{15})+\dfrac{3}{9}\times(\dfrac{2}{5})}\)

     B= \(\dfrac{\dfrac{3}{4}\times(\dfrac{-2}{15})}{\dfrac{2}{7}(-\dfrac{2}{15})+\dfrac{3}{9}\times\dfrac{2}{15}}\)

     B=\(\dfrac{\dfrac{3}{4}\times(\dfrac{-2}{15})}{\dfrac{2}{7}(\dfrac{-2}{15})+\dfrac{1}{3}\times\dfrac{2}{15}}\)

     B=\(\dfrac{\dfrac{3}{4}}{(\dfrac{2}{7}-\dfrac{1}{3})}\)

     B=\(\dfrac{\dfrac{3}{4}}{\dfrac{-1}{21}}\)

     B=\(\dfrac{3}{4}\times(\dfrac{-21}{1})\)

     B=\(\dfrac{63}{4}\)

Answer 30

B=63/52

A=5/4