Bài 1 :
a, $\frac{5}{8}$ - $\frac{2}{8}$ = $\frac{5-2}{8}$ = $\frac{3}{8}$
b, $\frac{11}{15}$ - $\frac{7}{15}$ = $\frac{11-7}{15}$ = $\frac{4}{15}$
c, $\frac{5}{7}$ - $\frac{12}{21}$ = $\frac{15}{21}$ - $\frac{12}{21}$ = $\frac{15-12}{21}$ = $\frac{3}{21}$ = $\frac{1}{7}$
d, $\frac{13}{9}$ - $\frac{28}{36}$ = $\frac{52}{36}$ - $\frac{28}{36}$ =$\frac{52-28}{36}$ = $\frac{24}{36}$ = $\frac{2}{3}$
Bài 2 :
a, $\frac{4}{7}$ + $\frac{3}{14}$ = $\frac{8}{14}$ + $\frac{3}{14}$ = $\frac{8+3}{14}$= $\frac{11}{14}$
b, $\frac{1}{12}$ + $\frac{3}{2}$ = $\frac{1}{12}$ + $\frac{18}{12}$ = $\frac{1+18}{12}$ = $\frac{19}{12}$
c, 5 + $\frac{3}{2}$ = $\frac{5}{1}$ + $\frac{3}{2}$ = $\frac{10}{2}$ + $\frac{3}{2}$ = $\frac{10+3}{2}$ = $\frac{13}{2}$
d, $\frac{4}{5}$ + $\frac{7}{3}$ = $\frac{12}{15}$ + $\frac{35}{15}$ = $\frac{12+35}{15}$ = $\frac{47}{15}$
