(158x168-79x58):11:10

=(26 544-4582):11:10

=21 962:11:10

=21 962/11:10

=10981/55

( 158 x 168 - 79 x 58 ) : 11 : 10 = ( 158 x 168 - 79 x 2 x 29) : 11 : 10

= ( 158 x 168 - 158 x 29) : 11 : 10

= 158 x ( 168 - 29 ) : 11 : 10

= 158 x 139 : 11 : 10

= 21962 : 11 : 10

= 10981/55

etwe

Đặt A = \(\dfrac{3}{6\cdot8}+\dfrac{3}{8\cdot10}+...+\dfrac{3}{158\cdot160}\)

A = \(\dfrac{3}{2}\cdot\left(\dfrac{2}{6\cdot8}+\dfrac{2}{8\cdot10}+...+\dfrac{2}{158\cdot160}\right)\)

A = \(\dfrac{3}{2}\cdot\left(\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{10}+...+\dfrac{1}{158}-\dfrac{1}{160}\right)\)

A = \(\dfrac{3}{2}\cdot\left(\dfrac{1}{6}-\dfrac{1}{160}\right)\)

A = \(\dfrac{3}{2}\cdot\dfrac{77}{480}\)

A = \(\dfrac{77}{320}\)

Vậy: A = \(\dfrac{77}{320}\)

Ta có : \(\frac{63}{31}=2\frac{1}{31};\frac{158}{51}=3\frac{5}{51};\frac{13}{21}2\frac{1}{31}>1\frac{17}{41}>\frac{13}{21}\)nên ta sắp xếp theo thứ tự giảm dần như sau :

\(3\frac{5}{51};2\frac{1}{31};1\frac{17}{41};\frac{13}{21}\)

(158 - 2\(\times\)\(x\)): 7 = 20

(158 - 2\(x\)) = 20 \(\times\) 7

158 - 2\(x\) = 140

          2\(x\) = 158 - 140

           2\(x\) = 18

              \(x\) = 18 : 2

              \(x\) = 9

(158-2*x):7=20

158-2*x=20*7

158-2*x=140

2*x=158-140

2*x=18

x=18:2

x=9

(158 - x) × 7 = 21

158 - x = 21 : 7

158 - x = 3

x = 158 - 3

x = 155

Vậy x = 155

thôi mình biết làm rùi

hihihi

a) \(128-3\cdot\left(x+4\right)=23\)

\(\Leftrightarrow3\cdot\left(x+4\right)=105\)

\(\Leftrightarrow x+4=35\)

\(\Leftrightarrow x=31\)

b) \(\left(158-x\right):7=20\)

\(\Leftrightarrow158-x=140\)

\(\Leftrightarrow x=18\)

\(a,128-3.\left(x+4\right)=23\)                                                      

\(\Rightarrow3.\left(x+4\right)=128-23\)

\(\Rightarrow3.\left(x+4\right)=105\)

\(\Rightarrow\left(x+4\right)=105:3\)

\(\Rightarrow\left(x+4\right)=35\)

\(\Rightarrow x=35-4\)

\(\Rightarrow x=31\)

Theo đề ta có : x = y + 25

Thay vào (x + y).2 = 158 ta đc :

(y + 25 + y).2= 158

=> 2y + 25 = 79

=> 2y = 54

=> y = 27

=> x = 27 + 25 = 52

Vậy x = 52 ; y = 27

X + Y = 158 : 2 = 79

X bằng: (79 + 25) : 2 = 52

Y bằng: 79 - 52 = 27

Biểu thức trên là: (52 + 27) x 2 = 158