a) $(\dfrac{7}{4}.\dfrac{-4}{5}+\dfrac{7}{2}.\dfrac{1}{5}).50$%$-0,1$
$=(\dfrac{-7}{5}+\dfrac{-7}{10}).\dfrac{1}{2}-\dfrac{1}{10}$
$=\dfrac{-7}{10}+\dfrac{-7}{20}-\dfrac{1}{10}$
$=(\dfrac{-7}{10}-\dfrac{1}{10})+\dfrac{-7}{20}$
$=\dfrac{-16}{20}+\dfrac{-7}{20}=\dfrac{-23}{20}$
b) $(2\dfrac{1}{3}+3\dfrac{1}{2}).0,2+25$%
$=(\dfrac{7}{3}+\dfrac{7}{2}).\dfrac{1}{5}+\dfrac{1}{4}$
$=\dfrac{7}{15}+\dfrac{7}{10}+\dfrac{1}{4}$
$=\dfrac{28}{60}+\dfrac{42}{60}+\dfrac{15}{60}$
$=\dfrac{28+42+15}{60}=\dfrac{17}{12}$