Đáp án:
128 - X : 12 = 97
X : 12 = 128 - 97
X : 12 = 31
X = 31 x 12
X = 372
X : $\frac{3}{4}$ + $\frac{4}{5}$ = $\frac{9}{10}$
X : $\frac{3}{4}$ = $\frac{9}{10}$ - $\frac{4}{5}$
X : $\frac{3}{4}$ = $\frac{1}{10}$
X = $\frac{1}{10}$ x $\frac{3}{4}$
X = $\frac{3}{40}$
X x $\frac{3}{5}$ + X + X x $\frac{2}{5}$ = $\frac{4}{7}$
X x ( $\frac{3}{5}$ + $\frac{2}{5}$ + 1 ) = $\frac{4}{7}$
X x 2 = $\frac{4}{7}$
X = $\frac{4}{7}$ : 2
X = $\frac{2}{7}$
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