Bài 1 :
a) $1$ - $\dfrac{1}{2}$ + $\dfrac{1}{3}$
= $\dfrac{1}{2}$ + $\dfrac{1}{3}$
= $\dfrac{5}{6}$
b) $\dfrac{2}{5}$ + $\dfrac{3}{5}$ : $\dfrac{9}{10}$
= $\dfrac{2}{5}$ + $\dfrac{2}{3}$
= $\dfrac{16}{15}$
c) $\dfrac{7}{11}$ . $\dfrac{3}{4}$ + $\dfrac{7}{11}$ . $\dfrac{1}{4}$ + $\dfrac{4}{11}$
= $\dfrac{7}{11}$ . ( $\dfrac{3}{4}$ + $\dfrac{1}{4}$ ) + $\dfrac{4}{11}$
= $\dfrac{7}{11}$ . $1$ + $\dfrac{4}{11}$ = $1$
d) ( $\dfrac{3}{4}$ + $0,5$ + $25$% ) . $2$$\dfrac{2}{3}$
= ( $\dfrac{3}{4}$ + $\dfrac{1}{2}$ + $\dfrac{1}{4}$ ) . $2$$\dfrac{2}{3}$
= ( $1$ + $\dfrac{1}{2}$ ) .$2$$\dfrac{2}{3}$
= $\dfrac{3}{2}$ . $2$$\dfrac{2}{3}$
= $4$
Bài 2 :
a) $x$ + $\dfrac{1}{2}$ = $2$
⇒ $x$ = $2$ - $\dfrac{1}{2}$ = $\dfrac{3}{2}$
b) $75$%$x$ - $\dfrac{1}{2}$ = $- 1$$\dfrac{1}{4}$
⇒ $75$%$x$ = $- 1$$\dfrac{1}{4}$ + $\dfrac{1}{2}$
⇒ $75$%$x$ = $\dfrac{-3}{4}$
⇒ $x$ = $\dfrac{-3}{4}$ : $75$%
⇒ $x$ = $- 1$
c) |$x$ - $\dfrac{2}{5}$ | + $\dfrac{7}{10}$ = $3$
⇒ | $x$ - $\dfrac{2}{5}$ | = $3$ - $\dfrac{7}{10}$ = $\dfrac{23}{10}$
⇒ $x$ \(\left[ \begin{array}{l}x- \dfrac{2}{5} = \dfrac{23}{10} \\x- \dfrac{2}{5} = \dfrac{-23}{10}\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x= \dfrac{27}{10} \\x= \dfrac{-19}{10} \end{array} \right.\)
