Exercício sobre álgebra elementar

(FUVEST) Calcule:

a)$\;\dfrac{1}{10}\;-\;\dfrac{1}{6}\;$

b)$\;\dfrac{0,2\; \centerdot\; 0,3}{3,2 \; \centerdot \; 2,0}\;$

resposta: a)-1/15 b)0,05

a)$\;\dfrac{3\,-\,5}{30}\,=\,\dfrac{-2}{30}\,=\;-\,\dfrac{1}{15}\;$
b)$\;\dfrac{0,06}{1,2}\,=\,\dfrac{6 \centerdot 10^{\large -2}}{12\centerdot 10^{\large -1}}\,=\;\dfrac{1}{20}\,=\,0,05\;$