a, $\dfrac{1}{13}-\dfrac{5}{18}+\dfrac{1}{5}+\dfrac{12}{13}-\dfrac{13}{18}$
$=(\dfrac{1}{13}+\dfrac{12}{13})+(\dfrac{-5}{18}-\dfrac{13}{18})+\dfrac{1}{5}$
$=1-1+\dfrac{1}{5}$
$=\dfrac{1}{5}$
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b, $\dfrac{-5}{13}.\dfrac{-17}{14}+\dfrac{-5}{13}.\dfrac{3}{14}$
$=\dfrac{-5}{13}(\dfrac{-17}{14}+\dfrac{3}{14})$
$=\dfrac{-5}{13}.-1$
$=\dfrac{5}{13}$
