1) 2,75 - 5/6 × 2/5 = 2,75 - (5/6) × (2/5) = 2,75 - 1/3 = 2,75 - 0,33 = 2,42

2) 1,25 - (5/6 - 0,75) - 3/5 = 1,25 - (5/6 - 0,75) - 3/5 = 1,25 - (5/6 - 3/4) - 3/5 = 1,25 - (5/6 - 9/12) - 3/5 = 1,25 - (10/12 - 9/12) - 3/5 = 1,25 - 1/12 - 3/5 = 1,25 - 0,08 - 0,6 = 1,25 - 0,68 = 0,57

3) 4/9 × 0,75 + 8/5 + 3,125 = (4/9) × 0,75 + 8/5 + 3,125 = 0,44 + 8/5 + 3,125 = 0,44 + 1,6 + 3,125 = 0,44 + 4,725 = 5,165

4) 1,125 - 4/7 - 0,12 = 1,125 - (4/7) - 0,12 = 1,125 - 0,57 - 0,12 = 0,435 - 0,12 = 0,315

5) (1/3 + 0,4) × 3,5 + (1/6 + 0,75) × 6/5

\(a,\left[0,75x+\frac{5}{2}\right]-\frac{4}{7}-\left[-\frac{1}{3}\right]=-\frac{5}{6}\)

\(\Leftrightarrow\left[0,75x+\frac{5}{2}\right]-\frac{4}{7}+\frac{1}{3}=-\frac{5}{6}\)

\(\Leftrightarrow\left[0,75x+\frac{5}{2}\right]=-\frac{5}{6}-\frac{1}{3}+\frac{4}{7}\)

\(\Leftrightarrow0,75x+\frac{5}{2}=-\frac{25}{42}\)

\(\Leftrightarrow0,75x=-\frac{65}{21}\Leftrightarrow x=-\frac{260}{63}\)

\(b,\left[4x-9\right]\left[2,5+-\frac{7}{3}x\right]=0\)

\(\Leftrightarrow\orbr{\begin{cases}4x-9=0\\2,5+-\frac{7}{3}x=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{9}{4}\\x=\frac{15}{14}\end{cases}}\)

Vậy \(x\in\left\{\frac{9}{4};\frac{15}{14}\right\}\)

Tham khảo nhé phamthiminhanh

\(\frac{3}{4}:\frac{x}{6}=0.75\)

\(\frac{3}{4}\cdot\frac{6}{x}=\frac{3}{4}\)

\(\frac{6}{x}=\frac{3}{4}:\frac{3}{4}\)

\(\frac{6}{x}=1\)

\(x=6\)

3/4 : x/6 = 0,75

        x/6 = 0,75 : 0,75 

        x/6 = 1 

        x   = 6

Hok tốt !!! 

                                                                                 ~~~ Mon ~~~

\(\frac{7}{12}x+0,75=-2\frac{1}{6}=-\frac{13}{6}\)

\(=>\frac{7}{12}x=-\frac{13}{6}-0,75=-\frac{13}{6}-\frac{3}{4}=-\frac{35}{12}\)

\(=>x=-\frac{35}{12}:\frac{7}{12}=-\frac{35}{12}.\frac{12}{7}=-\frac{35}{7}=-5\)

Vậy x=-5

\(-1<\frac{x}{4}<\frac{1}{2}\)

\(<=>-\frac{4}{4}<\frac{x}{4}<\frac{2}{4}\)

<=>-4<x<2

<=>x E {-3;-2;-1;0;1}

Vậy.......................

\(a)\frac{7}{12}x+0,75=-2\frac{1}{6}\)

\(\Rightarrow\frac{7}{12}x+\frac{3}{4}=-\frac{13}{6}\)

\(\Rightarrow\frac{7}{12}x=-\frac{13}{6}-\frac{3}{4}\)

\(\Rightarrow\frac{7}{12}x=-\frac{26}{12}-\frac{9}{12}\)

\(\Rightarrow\frac{7}{12}x=-\frac{35}{12}\)

\(\Rightarrow x=-\frac{35}{12}:\frac{7}{12}\)

\(\Rightarrow x=-\frac{35}{12}.\frac{12}{7}\)

\(\Rightarrow x=-5\)

\(b)-1< \frac{x}{4}< \frac{1}{2}\)

\(\Rightarrow-\frac{4}{4}< \frac{x}{4}< \frac{2}{4}\)

\(\Rightarrow-4< x< 2\)

\(\Rightarrow x\in\left\{-3;-2;-1;0;1\right\}\)

Chúc bạn học tốt !!! 

\(\frac{7}{12}x+0,75=-2\frac{1}{6}\)

\(\frac{7}{12}x=-\frac{13}{6}-\frac{3}{4}\)

\(\frac{7}{12}x=\frac{-35}{12}\)

\(x=\frac{-35}{12}:\frac{7}{12}\)

\(x=-5\)

b) \(-1< \frac{x}{4}< \frac{1}{2}\)

\(\frac{-4}{4}< \frac{x}{4}< \frac{2}{4}\)

\(\Rightarrow-4< x< 2\)

mà \(x\in Z\)  nên \(x\in\left\{-3;-2;\pm1;0\right\}\)

x +3x :2 =0,75

=>x +1,5x = 0,75

=>(1+1,5)x = 0,75

=>2,5x =0,75

=>x =0,3

(x + 3x) : 2 = 0,75

=> 4x = 0.75 . 2 

=> 4x = 1,5

=> x = 1,5 : 4

3 . x + 25% . x = -0,75

3 . x + 0,25 . x = -0,75

x . ( 3 + 0,25 ) = -0,75

x . 3,25 = -0,75

x         = -0,75 : 3,25

x          = \(-\frac{3}{13}\)

Bài 1

2/5 - 3/5 : (0,75 + 30%)

= 2/5 - 3/5 : 21/20

= 2/5 - 4/7

= -6/35

‐--------------------

Bài 2

a) x/6 = -11/3

x = -11/3 . 6

x = -22

b) 16/5 của x là 48

x = 48 : 16/5

x = 15

bài1

2/5-3/5:(0,75+30%)=2/5-3/5:(75/100+30/100)

                               =2/5-3/5:105/100

                               =2/5-3/5:21/20

                               = 2/5-3/5. 20/21

                               =2/5-1/1.4/7

                               =2/5-4/7

                               =2/5+-4/7

                               =14/35+-20/35

                               =34/35

− 1 4 + x + 0 , 75 = 3 1 2 → x = 7 2 − 3 4 + 1 4 → x = 3