Câu 1:
a) Ta có: \(\dfrac{3}{8}-\dfrac{1}{5}+1\dfrac{9}{20}\)
\(=\dfrac{3}{8}-\dfrac{1}{5}+\dfrac{29}{20}\)
\(=\dfrac{15}{40}-\dfrac{8}{40}+\dfrac{58}{40}\)
\(=\dfrac{65}{40}=\dfrac{13}{8}\)
Câu 1:
b) Ta có: \(\dfrac{-13}{7}:\dfrac{9}{17}+\dfrac{-13}{7}\cdot\dfrac{1}{9}+\dfrac{-13}{7}\)
\(=\dfrac{-13}{7}\cdot\dfrac{17}{9}+\dfrac{-13}{7}\cdot\dfrac{1}{9}+\dfrac{-13}{7}\)
\(=\dfrac{-13}{7}\left(\dfrac{17}{9}+\dfrac{1}{9}+1\right)\)
\(=-\dfrac{39}{7}\)
Câu 2:
a) Ta có: \(-0.1+x=\dfrac{2}{5}\)
\(\Leftrightarrow x=\dfrac{2}{5}+\dfrac{1}{10}=\dfrac{4}{10}+\dfrac{1}{10}=\dfrac{1}{2}\)
Vậy: \(x=\dfrac{1}{2}\)
