Đáp án:
a) ($\frac{1}{4}$ + x) x $\frac{1}{2}$ = $\frac{2}{5}$
($\frac{1}{4}$ + x) = $\frac{2}{5}$ : $\frac{1}{2}$
($\frac{1}{4}$ + x) = $\frac{2}{5}$ x 2
$\frac{1}{4}$ + x = $\frac{4}{5}$
x = $\frac{4}{5}$ - $\frac{1}{4}$
x = $\frac{16}{20}$ - $\frac{5}{20}$
x = $\frac{11}{20}$
Vậy x = $\frac{11}{20}$
b) x - 270 : 45 = 120
x - 6 = 120
x = 120 + 6
x = 126
Vậy x = 126
c) X x 15 - 3,7 = 2,3
X x 15 = 2,3 + 3,7
X x 15 = 6
X = 6 : 15
X = $\frac{6}{15}$
Vậy x = $\frac{6}{15}$
d) $\frac{8}{15}$ - $\frac{2}{15}$ : x = 0,2
$\frac{8}{15}$ - $\frac{2}{15}$ : x = $\frac{1}{5}$
$\frac{2}{15}$ : x = $\frac{8}{15}$ - $\frac{1}{5}$
$\frac{2}{15}$ : x = $\frac{8}{15}$ - $\frac{3}{15}$
$\frac{2}{15}$ : x = $\frac{1}{3}$
x = $\frac{2}{15}$ : $\frac{1}{3}$
x = $\frac{2}{15}$ x 3
x = $\frac{6}{15}$
Vậy x = $\frac{6}{15}$
