Ta có : (x + 3) + (x + 5) + (x + 7) + ..... + (x + 21) =  335

=> x + x + x + x + (3 + 5 + 7 + ..... + 21) = 335

=> 10x + 120 = 335

=> 10x = 335 - 120

=> 10x = 215

=> x = 21,5 

ta có : (x + 3) + (x + 5) + (x + 7) + ..... + (x + 21) =  335

<=> x + x + x + x + (3 + 5 + 7 + ..... + 21) = 335

<=> 10x + 120 = 335

=> 10x = 335 - 120

=> 10x = 215

vậy x = 21,5 

Ta có : |2x - 5| + |4 + x| = 0

Mà : |2x - 5| \(\ge0\forall x\)

       |4 + x| \(\ge0\forall x\)

Nên \(\orbr{\begin{cases}\left|2x-5\right|=0\\\left|4+x\right|=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}2x-5=0\\4+x=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}2x=5\\x=-4\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{5}{2}\\x=-4\end{cases}}\)

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) \(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\)

\(\Rightarrow\dfrac{5}{4}+x=\dfrac{5}{6}\)

\(\Rightarrow x=\dfrac{5}{6}-\dfrac{5}{4}\)

\(\Rightarrow x=\dfrac{-5}{12}\)

b) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\dfrac{-1}{3}\)

\(\Rightarrow x+\dfrac{1}{3}=\dfrac{11}{15}\)

\(\Rightarrow x=\dfrac{11}{15}-\dfrac{1}{3}\)

\(\Rightarrow x=\dfrac{2}{5}\)

c)\(\dfrac{-5}{8}-x=\dfrac{-3}{20}-\dfrac{-1}{6}\)

\(\dfrac{-5}{8}-x=\dfrac{1}{60}\)

\(\Rightarrow x=\dfrac{-5}{8}-\dfrac{1}{60}\)

\(\Rightarrow x=\dfrac{-77}{120}\)

d) \(\dfrac{3}{5}-x=\dfrac{1}{4}+\dfrac{7}{10}\)

\(\Rightarrow\dfrac{3}{5}-x=\dfrac{19}{20}\)

\(\Rightarrow x=\dfrac{3}{5}-\dfrac{19}{20}\)

\(\Rightarrow x=\dfrac{-7}{20}\)

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

\(\Rightarrow\dfrac{-3}{7}-x=\dfrac{2}{15}\)

\(\Rightarrow x=\dfrac{-3}{7}-\dfrac{2}{15}\)

\(\Rightarrow x=\dfrac{-59}{105}\)

g) \(\dfrac{-5}{6}-x=\dfrac{7}{12}+\dfrac{-1}{3}\)

\(\Rightarrow\dfrac{-5}{6}-x=\dfrac{1}{4}\)

\(\Rightarrow x=\dfrac{-5}{6}-\dfrac{1}{4}\)

\(\Rightarrow x=\dfrac{-13}{12}\)

[6: 3/5 - 7/6 x 6/7] : [ 21/5 x 10/11 + 57/11]

= 9 : 9

= 1 

\(\left(6:\frac{3}{5}-\frac{7}{6}\times\frac{6}{7}\right):\left(\frac{21}{5}\times\frac{10}{11}+\frac{57}{11}\right)\)

\(=\left(10-1\right):\left(\frac{42}{11}+\frac{57}{11}\right)\)

\(=9:9\)

\(=1\)

\(\left(6\div\frac{3}{5}-\frac{7}{6}\times\frac{6}{7}\right)\div\left(\frac{21}{5}\times\frac{10}{11}+\frac{57}{11}\right)\)

\(=\left(6\times\frac{5}{3}-1\right)\div\left(\frac{42}{11}+\frac{57}{11}\right)\)

\(=\frac{13}{5}\div9\)

\(=\frac{13}{45}\)

a: \(\Leftrightarrow5x=20\)

hay x=4

b: \(\Leftrightarrow x+7=24\)

hay x=17

1) \(5x-7=13\Rightarrow5x=13+7=20\Rightarrow x=20:5=4\)

2) \(\Rightarrow3\left(x+7\right)=95-23=72\)

\(\Rightarrow x+7=72:3=24\Rightarrow x=24-7=17\)

3) \(\Rightarrow2x+27=343\Rightarrow2x=343-27=316\Rightarrow x=316:2=158\)

+) 5x-7=13

5x=13+7

5x=20

x=20:5

x=4

+) 95-3(x+7)=23

3(x+7)=95-23

3(x+7)=72

x+7=72:3

x+7=24

x=24-7

x=17

+) 2x+3\(^2\).3=7\(^5\):7\(^2\)

2x+3\(^3\)=7\(^3\)

2x+27=343

2x=343-27

2x=316

x=316:2

x=158

1) 5|x-3| = \(\frac{5}{7}\)

=> |x-3| = \(\frac{1}{7}\)

\(\Rightarrow\orbr{\begin{cases}x-3=\frac{1}{7}\\x-3=\frac{-1}{7}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{22}{7}\\x=\frac{20}{7}\end{cases}}\)

Vậy x \(\in\){\(\frac{22}{7};\frac{20}{7}\)}

2) |x-11/7| = 0

=> x-11/7 = 0

=> x = 11/7

- Cía chỗ bài tìm x thứ 2 mình viết nhầm số 11/12 thành 11/7

2) |x-11/12|=0

=> x-11/12 = 0

=> x = 11/12

3/10 x 5/7 - 3/5 x 75/14

=3/14 - 45/14

= -3