a, Mẫu chung là \(24\)
\(\dfrac{1}{24}\\ \dfrac{1}{12}=\dfrac{1\times2}{12\times2}=\dfrac{2}{24}\)
b, Mẫu chung là :\(600\)
\(\dfrac{2}{30}=\dfrac{2.20}{30.20}=\dfrac{40}{600}\\ \dfrac{3}{40}=\dfrac{3.15}{40.15}=\dfrac{45}{600}\\ \dfrac{1}{50}=\dfrac{1.12}{50.12}=\dfrac{12}{600}\)