\(\dfrac{a}{b}=120\%\Leftrightarrow\dfrac{a}{b}=\dfrac{6}{5}\)
\(\Leftrightarrow\dfrac{a}{6}=\dfrac{b}{5}=\dfrac{a-b}{6-5}=\dfrac{-3}{1}=-3\)
\(\Rightarrow\dfrac{a}{6}=-3\Leftrightarrow a=-18\)
\(\dfrac{b}{5}=-3\Leftrightarrow b=-15\)
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