1. $\frac{1}{4}$$x$ - $\frac{2}{3}$= $\frac{5}{12}$
$\frac{1}{4}$$x$ = $\frac{5}{12}$ + $\frac{2}{3}$
$\frac{1}{4}$$x$ = $\frac{5}{12}$ + $\frac{8}{12}$
$\frac{1}{4}$$x$ = $\frac{13}{12}$
$x$ = $\frac{13}{12}$ : $\frac{1}{4}$
$x$ = $\frac{13}{12}$ . $4$
$x$ = $\frac{13}{3}$
2. $\frac{2}{5}$ - $x$= $\frac{7}{5}$
$x$= $\frac{2}{5}$ - $\frac{7}{5}$
$x$= $-1$
3. $\frac{5}{12}$$x$ + $\frac{3}{4}$= $\frac{1}{6}$
$\frac{5}{12}$$x$ = $\frac{1}{6}$ - $\frac{3}{4}$
$\frac{5}{12}$$x$ = $\frac{2}{12}$ - $\frac{9}{12}$
$\frac{5}{12}$$x$ = $\frac{-7}{12}$
$x$ =$\frac{-7}{12}$ : $\frac{5}{12}$
$x$ = $\frac{-7}{12}$ . $\frac{12}{5}$
$x$ = $\frac{-7}{5}$
4. $\frac{7}{4}$ - $x$= $-1$$\frac{7}{8}$
$\frac{7}{4}$ - $x$ = $\frac{-15}{8}$
$x$ = $\frac{7}{4}$ - $\frac{(-15)}{8}$
$x$ = $\frac{14}{8}$ - $\frac{-15}{8}$
$x$ = $\frac{29}{8}$
5. $x$ - $\frac{1}{2}$= $\frac{1}{3}$ + $\frac{1}{4}$
$x$ - $\frac{1}{2}$ = $\frac{4}{12}$ + $\frac{3}{12}$
$x$ - $\frac{1}{2}$ = $\frac{7}{12}$
$x$ = $\frac{7}{12}$ + $\frac{1}{2}$
$x$ = $\frac{7}{12}$ + $\frac{6}{12}$
$x$ = $\frac{13}{12}$
Cách tìm mẫu chung: Tìm BCNN của những số đó vì BCNN chính là mẫu chung.
