Đáp án:
$a. x = \frac{3}{20}$
$b. x = \frac{2}{5}$
$c. x = \frac{433}{210}$
$d. x = - \frac{39}{20}$
$e. x = \frac{41}{35}$
$f. x = \frac{3}{5}$
Giải thích các bước giải:
$a. \frac{-3}{5} - x = - 0,75$
⇔ $\frac{-3}{5} - x = \frac{-75}{100}$
⇔ $\frac{-3}{5} - x = \frac{-3×25}{4×25}$
⇔ $\frac{-3}{5} - x = \frac{-3}{4}$
⇔ $x = \frac{-3}{5} + \frac{3}{4}$
⇔ $x = \frac{-3×4+3×5}{5×4}$
⇔ $x = \frac{-12+15}{20}$
⇔ $x = \frac{3}{20}$
$b. x + \frac{1}{3} = \frac{2}{5} - (-\frac{1}{3})$
⇔ $x + \frac{1}{3} = \frac{2}{5} + \frac{1}{3}$
⇔ $x = \frac{2}{5} + \frac{1}{3} - \frac{1}{3}$
⇔ $x = \frac{2}{5}$
$c. 2\frac{1}{2} - x + \frac{4}{5} = \frac{2}{3} - (-\frac{4}{7})$
⇔ $\frac{5}{2} + \frac{4}{5} - x = \frac{2}{3} + \frac{4}{7}$
⇔ $\frac{5×5+4×2}{2×5} - x = \frac{2×7+4×3}{3×7}$
⇔ $\frac{25+8}{10} - x = \frac{14+12}{21}$
⇔ $\frac{33}{10} - x = \frac{26}{21}$
⇔ $x = \frac{33}{10} - \frac{26}{21}$
⇔ $x = \frac{33×21-26×10}{10×21}$
⇔ $x = \frac{693-260}{210}$
⇔ $x = \frac{433}{210}$
$d. 1\frac{4}{5} = - 0,15 - x$
⇔ $\frac{9}{5} = - \frac{15}{100} - x$
⇔ $\frac{9×4}{5×4} = - \frac{3×5}{20×5} - x$
⇔ $\frac{36}{20} = - \frac{3}{20} - x$
⇔ $x = - \frac{3}{20} - \frac{36}{20}$
⇔ $x = - \frac{39}{20}$
$e. - \frac{4}{7} - x = \frac{3}{5} - 2x$
⇔ $- x + 2x = \frac{3}{5} + \frac{4}{7}$
⇔ $x = \frac{3×7+4×5}{5×7}$
⇔ $x = \frac{21+20}{35}$
⇔ $x = \frac{41}{35}$
$f. ( \frac{3}{8} - \frac{1}{5} ) + ( \frac{5}{8} - x ) = \frac{1}{5}$
⇔ $\frac{3}{8} - \frac{1}{5} + \frac{5}{8} - x - \frac{1}{5} = 0$
⇔ $( \frac{3}{8} + \frac{5}{8} ) - \frac{2}{5} - x = 0$
⇔ $1 - \frac{2}{5} = x$
⇔ $x = \frac{3}{5}$
