d)$\frac{1}{2}$ ;$\frac{1}{3}$ ;$\frac{2}{5}$ (MSC= 30) vì chỉ có 30 là chia hết cho cả ba số trên
$\frac{1}{2}$= $\frac{1*15}{2*15}$ =$\frac{15}{30}$
$\frac{1}{3}$ =$\frac{1*10}{3*10}$ = $\frac{10}{30}$
$\frac{2}{5}$ =$\frac{2*6}{5*6}$ =$\frac{12}{30}$
e)$\frac{1}{4}$ ;$\frac{3}{5}$ ;$\frac{17}{20}$ (MSC:20)
$\frac{1}{4}$ =$\frac{1*5}{4*5}$ =$\frac{5}{20}$
$\frac{3}{5}$= $\frac{3*4}{5*4}$ =$\frac{12}{20}$
giữ nguyên $\frac{17}{20}$
3.
$\frac{3}{5}$ =$\frac{12}{20}$ =$\frac{60}{100}$ $\frac{6}{7}$ =$\frac{12}{24}$ =$\frac{18}{21}$
4.
$\frac{15}{40}$ =$\frac{15:5}{40:5}$ =$\frac{3}{8}$
$\frac{21}{39}$ =$\frac{21:3}{39:3}$ =$\frac{7}{13}$
$\frac{16}{24}$ =$\frac{16:8}{24:8}$ =$\frac{2}{3}$
$\frac{36}{72}$ =$\frac{36:36}{72:36}$ =$\frac{1}{2}$ $\frac{24}{100}$ =$\frac{24:4}{100:4}$ $\frac{6}{25}$
