a) +) \(\dfrac{2}{3}+ \dfrac{3}{5} = \dfrac{10}{15} + \dfrac{9}{15}= \dfrac{19}{15}\);
+) \(\dfrac{7}{12}- \dfrac{2}{7}+ \dfrac{1}{12} = \dfrac{49}{84} - \dfrac{24}{84} + \dfrac{7}{84}\)
\(= \dfrac{25}{84}+ \dfrac{7}{84} = \dfrac{32}{84} = \dfrac{8}{21}\);
+) \(\dfrac{12}{17}- \dfrac{5}{17} - \dfrac{4}{17}= \dfrac{7}{17} - \dfrac{4}{17} = \dfrac{3}{17}\).
b) +) \(578,69 + 281,78 = 860,47\);
+) \(594,72 + 406,38 - 329,47 \) \(= 1001,1 - 329,47 = 671,63\).
