a. \(\frac{4}{25}\times72+\frac{4}{25}\times28=\frac{4}{25}\times\left(72+28\right)=\frac{4}{25}\times100=4\times4=16\)

b.\(0.5\times72+\frac{3}{6}\times28=0.5\times72+0.5\times28=0.5\times\left(72+28\right)=0.5\times100=50\)

a) 4/25 × 72 + 4/25 × 28

= 4/25 × (72+28)

= 4/25 × 100

= 16/100 × 100

= 16

b) 0.5 × 72 + 3/6 × 28

= 5/10 × 72 + 3/6 × 28

= 1/2 × 72 + 1/2 × 28

= 1/2 × (72 + 28)

= 1/2 × 100

= 5/10 × 100

= 50

các bạn làm ơn giúp mình với đc ko , mình đang cần gấp !!!! 

Trả lời:

\(A=\frac{6}{8}.\frac{8}{13}+\frac{6}{13}.\frac{9}{7}-\frac{3}{13}.\frac{6}{7}\)

\(A=\frac{6}{13}+\frac{54}{91}-\frac{18}{91}\)

\(A=\frac{6}{7}\)

\(B=\left(\frac{5}{4}+\frac{3}{4}\right).\frac{4}{7}.\left(\frac{3}{4}+\frac{9}{4}\right).\frac{4}{7}\)

\(B=\frac{2}{1}.\frac{4}{7}.\frac{3}{1}.\frac{4}{7}\)

\(B=\frac{8}{7}.\frac{12}{7}\)

\(B=\frac{96}{49}\)

Help

a) 1+2+3+4+5+6+7+8+9

= (1+9)+(2+8)+(3+7)+(4+6)+5

= 10+10+10+10=5

= 45

b) 19+28+37+46+81+72+63+54

= (19+81)+(28+72)+(46+54)+(63+37)

= 100+100+100+100

= 400

`#3107.101107`

\(-16 \div (-8)+5[3-15\div5+2(-3+4)]\)

`= 2 + 5(3 - 3 - 6 + 8)`

`= 2 + 5*(-6 + 8)`

`= 2 + 5*2`

`= 2(5 + 1)`

`= 2*6 = 12`

____

`15*(-236)+15*235`

`= 15 * (-236 + 235)`

`= 15 * (-1)`

`= -15`

____

`237*(-28)+28*137`

`= 28 * (-237 + 137)`

`= 28 * (-100)`

`= -2800`

____

`(-3)*(-17)+3*(120-17)`

`= 3 * 17 + 3 * (120 - 17)`

`= 3 * (17 + 120 - 17)`

`= 3 * 120`

`= 360`

____

`(-8)*72+8*(-19)-(-8)`

`= 8 * (-72) + 8 * (-19) + 8`

`= 8 * (-72 - 19 + 1)`

`= 8 * (-90)`

`= -720`

a,280:  (7 + 3 : x ) = 4

             (7 + 3 : x ) = 280:4

              ( 7+ 3: x)  =70

               3 : x  = 70-7

                3:x=63

                   x=63.3

                   x=   189

b,(x+5).19:13=57

    (x+5).19  =57.13

     (x+5).19  =741

      (x+5)    =741:19

       (x+5)   =39

        x=39-5

       x = 34

c,6.(28-8.x)=72

      (28-8.x)=72:6

      (28-8.x)=12

            8x=28-12

             8x=16

             x=16:8

           X=2

a) (x.7 + 8) : 5 = 10

x.7 + 8 = 10.5

x.7 + 8 = 50

x.7 = 50 - 8

x.7 = 42

x = 42 : 7

x = 6

b) (x + 5).19 : 13 = 57

(x + 5).19 = 57 . 13

(x + 5).19 = 741

x + 5 = 741 : 19

x + 5 = 39

x = 39 - 5

x = 34

c) 4.(36 - 4.x) = 64

36 - 4x = 64 : 4

36 - 4x = 16

4x = 36 - 16

4x = 20

x = 20 : 4

x = 5

d) 7,6 : 19 . x = 3,2

0,4 . x = 3,2

x = 3,2 : 0,4

x = 8

e) (x : 2 + 50) : 5 = 12

x : 2 + 50 = 12 . 5

x : 2 + 50 = 60

x : 2 = 60 - 50

x : 2 = 10

x = 10 . 2

x = 20

g) 280 : (17 + 3.x) = 4

17 + 3x = 280 : 4

17 + 3x = 70

3x = 70 - 17

3x = 53

x = 53/3

h) 6.(28 - 8.x) = 72

28 - 8x = 72 : 6

28 - 8x = 12

8x = 28 - 12

8x = 16

x = 16 : 8

x = 2

i) (x - 15) : 3 : 12 = 6

(x - 15) : 3 = 6 . 12

(x - 15) : 3 = 72

x - 15 = 72 . 3

x - 15 = 216

x = 216 + 15

x = 231