Bài 4:
\(\dfrac{1}{4}=\dfrac{1\cdot9}{4\cdot9}=\dfrac{9}{36};\dfrac{2}{9}=\dfrac{2\cdot4}{9\cdot4}=\dfrac{8}{36}\)
\(\dfrac{5}{12}=\dfrac{5\cdot3}{12\cdot3}=\dfrac{15}{36};\dfrac{4}{36}=\dfrac{4\cdot1}{36\cdot1}=\dfrac{4}{36}\)
Vì \(\dfrac{15}{36}>\dfrac{9}{36}>\dfrac{8}{36}>\dfrac{4}{36}\)
nên lớp trưởng sẽ là bạn Ngọc