b: =15/31(34/63-11/21)=15/31x1/63=5/651

a: \(=\dfrac{67}{63}\cdot5+\dfrac{11}{31}\cdot\dfrac{5}{7}=5\left(\dfrac{67}{63}+\dfrac{11}{31\cdot7}\right)=\dfrac{10880}{1953}\)

b: =15/31(34/63-11/21)=15/31x1/63=5/651

a: 

a) 21/11 x 22/17 x 68/63 = 21 x 22 x 68/11 x 17 x 63 = 1 x 2 x4/1 x 1 x 3= 8/3

b) kết quả là 2/10 = 1/5

         phần b làm như phần a

a) = \(\frac{21\cdot22\cdot68}{11\cdot17\cdot63}\)=\(\frac{1\cdot2\cdot4}{2\cdot1\cdot3}\)=\(\frac{4}{3}\)

b) = \(\frac{5\cdot7\cdot26}{14\cdot13\cdot25}\)=\(\frac{1\cdot1\cdot2}{2\cdot1\cdot5}\)=\(\frac{1}{5}\)

\(\frac{21}{11}\times\frac{22}{17}\times\frac{68}{63}\)

\(=\frac{21}{1}\times\frac{2}{1}\times\frac{4}{63}\)

\(=42\times\frac{4}{63}\)

\(=\frac{168}{63}\)

dấu . là nhân hay là phần ngăn cách ở hàng phần nghìn thế

a) \(28400:\left(100\times311-310\times100\right)\)
\(=28400:\left[\left(311-310\right)\times100\right]\)
\(=28400:100\)
\(=284\)
b) \(\dfrac{5}{11}+\dfrac{19}{15}+\dfrac{6}{11}+\dfrac{11}{16}+\dfrac{6}{15}+\dfrac{5}{16}\)
\(=\left(\dfrac{5}{11}+\dfrac{6}{11}\right)+\left(\dfrac{19}{15}+\dfrac{6}{15}\right)+\left(\dfrac{11}{16}+\dfrac{5}{16}\right)\)
\(=1+\dfrac{5}{3}+1\)
\(=\dfrac{8}{3}+1\)
\(=\dfrac{11}{3}\)

a) 28.400 : ( 100 x 311 - 310 x 100 )     

= 28.400 :  [ 100 x ( 311 - 310  ]

= 28.400 : 100 x 1

= 0.284 x 1

= 0.284

b) \(\dfrac{5}{11}+\dfrac{19}{15}+\dfrac{6}{11}+\dfrac{11}{16}+\dfrac{6}{15}+\dfrac{5}{16}\)

\(=\left(\dfrac{5}{11}+\dfrac{6}{11}\right)+\left(\dfrac{19}{15}+\dfrac{6}{15}\right)+\left(\dfrac{11}{16}+\dfrac{5}{16}\right)\)

\(=1+\dfrac{5}{3}+1\)

\(=\dfrac{11}{3}\)

a) 15/21 + 7/21 + 5/21

= (15/21 + 5/21) + 7/21

= 20/21 + 7/21

= 27/21

b) 4/7 + 8/15 + 22/15

= 4/7 + 2

= 18/7

nha bn

a,\(\frac{15}{21}+\frac{7}{21}+\frac{5}{21}\)

= \(\left(\frac{15}{21}+\frac{5}{21}\right)+\frac{7}{21}\)

=  \(\frac{20}{21}+\frac{7}{21}\)

=\(\frac{27}{21}\)

b, \(\frac{4}{7}+\frac{8}{15}+\frac{22}{15}\)

=\(\frac{4}{7}+\left(\frac{8}{15}+\frac{22}{15}\right)\)

= \(\frac{4}{7}+2\)

= \(\frac{18}{7}\)

5/11.5/7+2/7.5/11

=5/11.(5/7+2/7)

=5/11

15 x 7/15 x 4/9

=7 x 4/9

=28/9

5/11

28/9

(36 × 27) : 3 = 36 × (27 : 3)

= 36 × 9

= 324

--------

(125 × 15) : 5

= 125 × (15 : 5)

= 125 × 3

= 375

--------

(15 × 12) : 9

= (5 × 3 × 12) : 9

= 5 × (36 : 9)

= 5 × 4

= 20

--------

450 : (3 × 5)

= 450 : 15

= 30

--------

(45 × 63) : 9

= 45 × (63 : 9)

= 45 × 7

= 40 × 7 + 5 × 7

= 280 + 35

= 315

a: \(\dfrac{\left(36\cdot27\right)}{3}=36\cdot\dfrac{27}{3}=36\cdot9=324\)

b: \(\dfrac{\left(125\cdot15\right)}{5}=125\cdot\dfrac{15}{5}=125\cdot3=375\)

c: \(\dfrac{\left(15\cdot12\right)}{9}=\dfrac{3\cdot3\cdot4\cdot5}{9}=4\cdot5=20\)

d: \(\dfrac{450}{3\cdot5}=\dfrac{450}{15}=30\)

e: \(\dfrac{45\cdot63}{9}=\dfrac{45}{9}\cdot63=63\cdot5=315\)

Ta có: \(\frac{3}{7}x\frac{21}{15}:\frac{3}{5}=\frac{3}{7}x\frac{21}{15}x\frac{5}{3}=\frac{3x21x5}{7x15x3}\)\(=\frac{3x3x7x5}{7x3x5x3}=1\)

Mọi người tk cho mình nha. Mình cảm ơn nhiều ^-^

3/7x3x7/3x5:3/5

=3/7x3x7/3x5;3/5

3/5:3/5=1

\(\frac{3}{7}x\frac{21}{15}:\frac{3}{5}\)

= \(\frac{3}{5}:\frac{3}{5}\)

= 1

                          Nếu các bn thấy đúng thì **** mk heg..........♥♥♥♥♥

                             Ai tk mk mk tk lại ~   ♥♥♥♥

                                   ! chúc ai tk mk thi tốt ~ ♥♥♥♥

dài quá làm hộ câu 1-5 thoy

1) x=21-13 

    x=8

2)x=-55+41

   x=-14

3)x=-21+15

    x=-6

4)x=3-3

    x=0

5) x= -98-37

   x=-135

15 ) 57 - ( x - 46 ) = - 13

       57 - x + 46 = -13

       103 - x = -13

       x  = 103 + 13

       x  =  116

16 ) -x - 23 = -38 - 42

       - ( x + 23 )=- ( 38 + 42)

            x + 23 = 38 + 42

             x       = 38 + 42 -23

              x      =  57

17 ) x - ( - 7 ) = -4 – 14

      X + 7 = -18

       X = -18-7

        X  = -25

18 ) 18 - x = -8 - ( - 15 )

       18 – x = 7

               X = 18 – 7

                X = 11

19 ) 45 - (  x + 17 ) = - 26

        45 – x - 17  = -26

        28 – x = -26

                X = 28 + 26

                X = 54

20 ) 3. ( x + 5 ) - x - 11 = 24

       3x +15 –x – 11 = 24

       2x + 4 =24

        2x = 24 – 4

        2x = 20

          X = 20 : 2

         X = 10

21 ) 14 - ( x - 7 ) = - 8 - ( - 9 )

       14 – x + 7 = 1

       21 – x = 1

               X = 21 – 1

               X = 20

22 ) 15 - ( x - 2 ) =  - 7 + 8

         15 – x + 2 = 1

            17 – x = 1

                    X = 17 – 1

                    X = 16

6)  x + ( - 71 ) = ( - 55 ) + 85 

      X – 71 = 30

      X = 30 + 71

      X = 101

7 ) x - ( - 45 ) = - 63 + 27

 X +45 = -16

 X = -16 -45

X = - 61

6)  x + ( - 71 ) = ( - 55 ) + 85

X=30+71=101

7 ) x - ( - 45 ) = - 63 + 27

X=-36-45=-81

8) x + 29 = 43 + ( - 23 )

X=20-29=-9

9 ) x + ( - 47 ) = ( - 62 ) – 17

X=-79+47=-32

10 ) x + 21 = ( - 43 ) + 43

X=0-21=-21

11 ) 31 + x = 45 – 81

 X=-36-31=-67

12 ) x - 12 = ( - 8 ) + (- 7 )

 X=-15+12=-3

13 ) 23 - x = 24 - ( - 16 )

X=23-40=-17

14 ) - 15 - ( - 21 - 3x ) = - 63 -15+21+3x=-63 21+3x=-63-(-15)

 21+3x=-48

3x=-48-21

3x=-69

X=-69 : 3

X=-23