Câu 13. \(\dfrac{7}{24}=\dfrac{35}{120};\dfrac{3}{40}=\dfrac{9}{120};\dfrac{1}{30}=\dfrac{4}{120};\dfrac{11}{60}=\dfrac{22}{120}.\)Câu 14.\(\dfrac{3}{4}=\dfrac{60}{80};\dfrac{12}{7}=\dfrac{60}{35};\dfrac{6}{5}=\dfrac{60}{50};\dfrac{15}{17}=\dfrac{60}{68};\dfrac{20}{31}=\dfrac{60}{93}.\)Câu 15. \(a.\dfrac{3\times4\times8\times9\times10}{4\times8\times9\times10\times13}=\dfrac{3}{13}.\)\(b.\dfrac{3\times145+3\times55}{6\times215+6\times85}=\dfrac{3\times\left(145+55\right)}{6\times\left(215+85\right)}=\dfrac{3\times200}{6\times300}=\dfrac{1}{3}.\)Câu trả lời: Câu 13. \(\dfrac{7}{24}=\dfrac{35}{120};\dfrac{3}{40}=\dfrac{9}{120};\dfrac{1}{30}=\dfrac{4}{120};\dfrac{11}{60}=\dfrac{22}{120}.\)Câu 14.\(\dfrac{3}{4}=\dfrac{60}{80};\dfrac{12}{7}=\dfrac{60}{35};\dfrac{6}{5}=\dfrac{60}{50};\dfrac{15}{17}=\dfrac{60}{68};\dfrac{20}{31}=\dfrac{60}{93}.\)Câu 15. \(a.\dfrac{3\times4\times8\times9\times10}{4\times8\times9\times10\times13}=\dfrac{3}{13}.\)\(b.\dfrac{3\times145+3\times55}{6\times215+6\times85}=\dfrac{3\times\left(145+55\right)}{6\times\left(215+85\right)}=\dfrac{3\times200}{6\times300}=\dfrac{1}{3}.\)