1/ MSC: $24$
$\dfrac{3}{-8}=\dfrac{3.(-3)}{(-8).(-3)}=\dfrac{-9}{24}$
$\dfrac{-7}{2}=\dfrac{-7.12}{2.12}=\dfrac{-84}{24}$
$\dfrac{2}{3}=\dfrac{2.8}{3.8}=\dfrac{18}{24}$
$\dfrac{5}{6}=\dfrac{5.4}{6.4}=\dfrac{20}{24}$
Sắp xếp theo thứ tự từ lớn đến bé: $\dfrac{20}{24};\dfrac{18}{24};\dfrac{-9}{24};\dfrac{-84}{24}$
hay: $\dfrac{5}{6};\dfrac{2}{3};\dfrac{3}{-8};\dfrac{-7}{2}$
2/
$75\%+1,1:\bigg(\dfrac{2}{5}-1\dfrac{1}{2}\bigg)-\bigg(\dfrac{1}{3}\bigg)^2$
$=\dfrac{3}{4}+\dfrac{11}{10}:\bigg(\dfrac{2}{5}-\dfrac{3}{2}\bigg)-\dfrac{1}{9}$
$=\dfrac{3}{4}+\dfrac{11}{10}:\dfrac{-11}{10}-\dfrac{1}{9}$
$=\dfrac{3}{4}-1-\dfrac{1}{9}$
$=\dfrac{-13}{36}$
3/
$\dfrac{12}{19}.\dfrac{7}{15}.\dfrac{-13}{17}.\dfrac{19}{12}.\dfrac{17}{13}$
$=\bigg(\dfrac{12}{19}.\dfrac{19}{12}\bigg).\dfrac{7}{15}.\bigg(\dfrac{-13}{17}.\dfrac{17}{13}\bigg)$
$=1.\dfrac{7}{15}.(-1)$
$=\dfrac{-7}{15}$
