Bài 1:
1) Ta có: \(21+\left(-18\right)+29+\left(-42\right)\)
\(=21-18+29-42\)
\(=50-42-18\)
=-10
Bài 1:
2) Ta có: \(351-\left(-278+351\right)-\left(278-20\right)\)
\(=351+278-351-278+20\)
=20
Bài 1:
3) Ta có: \(\dfrac{-17}{30}-\dfrac{11}{-15}+\dfrac{-7}{12}\)
\(=\dfrac{-34}{60}+\dfrac{44}{60}+\dfrac{-35}{60}\)
\(=\dfrac{-25}{60}=\dfrac{-5}{12}\)
Bài 1:
4) Ta có: \(\dfrac{-5}{9}+\dfrac{5}{9}\left(1\dfrac{2}{3}-2\dfrac{1}{12}\right)\)
\(=\dfrac{5}{9}\left(-1+\dfrac{5}{3}-\dfrac{25}{12}\right)\)
\(=\dfrac{5}{9}\left(\dfrac{-12}{12}+\dfrac{20}{12}-\dfrac{25}{12}\right)\)
\(=\dfrac{5}{9}\cdot\dfrac{-17}{12}=\dfrac{-85}{108}\)
