a: \(\dfrac{18}{20}=\dfrac{18:2}{20:2}=\dfrac{9}{10}\)
\(\dfrac{9}{12}=\dfrac{9:3}{12:3}=\dfrac{3}{4}\)
\(\dfrac{30}{25}=\dfrac{30:5}{25:5}=\dfrac{6}{5}\)
\(\dfrac{36}{45}=\dfrac{36:9}{45:9}=\dfrac{4}{5}\)
b: \(\dfrac{50}{60}=\dfrac{50:10}{60:10}=\dfrac{5}{6}\)
\(\dfrac{42}{48}=\dfrac{42:6}{48:6}=\dfrac{7}{8}\)
\(\dfrac{60}{45}=\dfrac{60:15}{45:15}=\dfrac{4}{3}\)
\(\dfrac{18}{54}=\dfrac{18:18}{54:18}=\dfrac{1}{3}\)