a) 

(1/3-1/5)x1/4 = 1/3x1/4-1/5x1/4=1/12-1/20=1/30

(1/3-1/5)x1/4 = 2/15x1/4=1/30

b)

2/5 x 3/7 + 2/5 x 4/7= 6/35 + 8/35 = 14/35 = 2/5

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

a: C1: (1/3-1/5)*1/4

=2/15*1/4=2/60=1/30

C2: (1/3-1/5)*1/4

=1/3*1/4-1/5*1/4

=1/12-1/20=1/30

b: C1: 2/5*3/7+2/5*4/7

=6/35+8/35=14/35=2/5

C2: 2/5*3/7+2/5*4/7

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

=2/5*1=2/5

a)

C1: 4✖5✖3                           C2:4✖5✖3          

=20✖3                                   =12✖5

=60                                         =60

b)

C1: 3✖5✖6                         C2:3✖5✖6      

=15✖6                                  =18✖5

=90                                        =90

Tính thuận tiện

a)13✖5✖2                         b)5✖2✖34

=13✖10                              =10✖34

=130                                   =340

tính bằng 2 cách:
a.4 nhân 5 nhân 3

C1 : 4 x 5 x 3

 = 20 x 3

 = 60

C2 : 4 x 5 x 3

= ( 4 x 5 ) x 3

= 20 x 3

= 60
b.3 nhân 5 nhân 6

C1 : 3 x 5 x 6

= 15 x 6

= 90

C2 : 3 x 5 x 6

= 3 x ( 5 x 6 )

= 3 x 30

= 90
tính bằng cách thuận tiện nhất:
a.13 nhân 5 nhân 2

13 x 5 x 2

= 13 x ( 5 x 2 )

= 13 x 10

= 130
b.5 nhân 2 nhân 34

5 x 2 x 34

= ( 5 x 2 ) x 34

= 10 x 34

= 340

/:)))

???

Jjj

a) \(\dfrac{3}{5}:\left(\dfrac{7}{11}+\dfrac{4}{11}\right)=\dfrac{3}{5}.1=\dfrac{3}{5}\)

 c2: \(\dfrac{7}{11}:\dfrac{3}{5}+\dfrac{4}{11}:\dfrac{3}{5}=\dfrac{7}{11}.\dfrac{5}{3}+\dfrac{4}{11}.\dfrac{5}{3}=\dfrac{3}{5}\)

a) 

C1: \(\dfrac{7}{11}:\dfrac{3}{5}+\dfrac{4}{11}:\dfrac{3}{5}=\left(\dfrac{7}{11}+\dfrac{4}{11}\right):\dfrac{3}{5}=1:\dfrac{3}{5}=\dfrac{5}{3}\)

O ở chỗ đáp án là độ nha

ghi nhiều quá

a)1440:40 =36

b)205 x 13 =2665

c)2057

d)36 x 25 x 4 =3600

18 x 24 :9 =48

41 x 2 x 8 x 5 =3280

215 x 86 + 215 x 14 =21500

53 x 128 - 43 x 128 =1408

2/3 x 4/7 =8/21

2 x 3 x 4 / 2 x 3 x 4 x 5 =24/120

1 x 2 x 3 x 4  / 5 x 6 x 7 x 8=24/1680

x : 7/11 = 22

          x =22 x 7/11

          x =14

2/7 * x =2/3 

         x = 2/7 :2/3

         x = 20/21

20/21     zxhbhs

C1:

a)    135  x   54    +    45    x  135    +   135

= 135 x ( 54 + 45 + 1)

=135x100=13500

C2

a)    135  x   54    +    45    x  135    +   135

= 7290 + 6075 +135

= 13500

\(12\left(x+5\right)+2x=130\\\Leftrightarrow 12x+60+2x=130\\ \Leftrightarrow14x=70\\ \Leftrightarrow x=5\\ ----\\ 23\left(x-5\right)-12x=138\\ \Leftrightarrow23x-115-12x=138\\ \Leftrightarrow23x-12x=138+115\\ \Leftrightarrow11x=253\\ \Leftrightarrow x=\dfrac{253}{11}=23\\ ----\\ 360-12x+23\left(x-5\right)=278\\ \Leftrightarrow360-12x+23x-115=278\\ \Leftrightarrow-12x+23x=278+115-360\\ \Leftrightarrow11x=33\\ \Leftrightarrow x=\dfrac{33}{11}=3\)

\(6\left(x+3\right)+3\left(x-5\right)=278\\ \Leftrightarrow6x+18-3x-15=278\\ \Leftrightarrow6x-3x=278+15-18\\ \Leftrightarrow3x=275\\ \Leftrightarrow x=\dfrac{275}{3}\\ ---\\ \left(7-x\right)\left(3x-90\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}7-x=0\\3x-90=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=7\\x=30\end{matrix}\right.\)

\(\left(x-2\right)\left(4x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-2=0\\4x-2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\4x=2\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{1}{2}\end{matrix}\right.\\ ---\\ \left(2x-18\right)\left(3x-9\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}2x-18=0\\3x-9=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=18\\3x=9\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=9\\x=3\end{matrix}\right.\)

a) 1440: [41-{2x-5}]=16.3

    41-(2x-5)=1440-48

   41-(2x-5)=1392

     2x-5=41-1392

     2x-5=-1351

        2x=-1351+5

        2x=-1346

         x=(-1346):2

         x=-673

b) 5.[225-(x-10)]-125=0

      5.[225-(x-10)=0+125

          225-(x-10)=125:5

          225-(x-10)=25

                x-10=225-25

               x-10=200

               x=200+10

             x=210

c) x thuộc {1,2,3,6}