Cálculos combinados | Práctica 0 ejercicio 1b

EJERCICIO 1:Calcule

(b) $\dfrac{2}{5}+ (-2)\left(-\dfrac{1}{2}+1-(\dfrac{1}{5}-\dfrac{3}{10})-\dfrac{1}{4}\right)$

Solución:

$\dfrac{2}{5}+ (-2)\left(-\dfrac{1}{2}+1-(\dfrac{2-3}{10})-\dfrac{1}{4}\right)=$

$\dfrac{2}{5}-2\cdot\left(-\dfrac{1}{2}+1+\dfrac{1}{10}-\dfrac{1}{4}\right)=$

$\dfrac{2}{5}-2\cdot\left(\dfrac{-10+20+2-5}{20}\right)=$

$\dfrac{2}{5}-2\cdot\left(\dfrac{7}{20}\right)=$

$\dfrac{2}{5}-\left(\dfrac{\cancel{14}^{7}}{\cancel{20}_{10}}\right)=$

$\dfrac{2}{5}-\left(\dfrac{7}{10}\right)= \dfrac{4-7}{10} = \boxed{-\dfrac{3}{10}}$