a) \(\dfrac{-0.8:\left(\dfrac{4}{5}\cdot1.25\right)}{0.64-\dfrac{1}{5}}=\dfrac{\dfrac{-4}{5}:\left(\dfrac{4}{5}\cdot\dfrac{5}{4}\right)}{\dfrac{16}{25}-\dfrac{1}{5}}=\dfrac{\dfrac{-4}{5}:1}{\dfrac{16}{25}-\dfrac{5}{25}}=\dfrac{\dfrac{-4}{5}}{\dfrac{11}{25}}=\dfrac{-4}{5}\cdot\dfrac{25}{11}=\dfrac{-20}{11}\)
b) \(\left(13.71-1\dfrac{5}{6}\right)\cdot6-6\cdot13\cdot17=\left(\dfrac{1371}{100}-\dfrac{11}{6}\right)\cdot6-6\cdot13\cdot17=\dfrac{3563}{300}\cdot6-6\cdot13\cdot17=\dfrac{3563}{50}-6\cdot13\cdot17=\dfrac{3563}{50}-1326=\dfrac{-62737}{50}\)
c) \(\dfrac{\left(\dfrac{3}{5}+0.415+\dfrac{1}{200}\right):0.01}{30.75+\dfrac{1}{12}+3\dfrac{1}{6}}=\dfrac{\left(\dfrac{3}{5}+\dfrac{83}{200}+\dfrac{1}{200}\right):\dfrac{1}{100}}{\dfrac{123}{4}+\dfrac{1}{12}+\dfrac{19}{6}}=\dfrac{\dfrac{51}{50}:\dfrac{1}{100}}{34}=\dfrac{102}{34}=3\)
