Câu 21 :
\(\dfrac{5}{9}.\dfrac{14}{17}+\dfrac{1}{17}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{5}{17}\)\(=\dfrac{5}{9}\left(\dfrac{14}{17}+\dfrac{1}{17}+\dfrac{5}{17}\right)=\dfrac{5}{9}.\dfrac{20}{17}=\dfrac{100}{153}\)
Câu 22:
\(x-\dfrac{1}{2}=\dfrac{-16}{5}.\dfrac{1}{2}\)
\(x-\dfrac{1}{2}=\dfrac{-8}{5}\)
\(x=\dfrac{-8}{5}+\dfrac{1}{2}\)
\(x=\dfrac{-13}{10}\)
Câu 23: