Bài 1: xem hình
Bài 2:
a)$\frac{21}{23}$-($\frac{7}{32}$+$\frac{8}{23}$)= $\frac{21}{23}$-$\frac{7}{32}$-$\frac{8}{23}$=($\frac{21}{23}$-$\frac{8}{23}$)-$\frac{7}{32}$=$\frac{13}{23}$-$\frac{7}{32}$= $\frac{255}{736}$
b)$\frac{38}{45}$ - ($\frac{8}{45}$- $\frac{17}{51}$- $\frac{3}{11}$)= $\frac{38}{45}$ - $\frac{8}{45}$+ $\frac{17}{51}$+ $\frac{3}{11}$=$\frac{30}{45}$+ $\frac{17}{51}$+ $\frac{3}{11}$=$\frac{2}{3}$+ $\frac{1}{3}$+ $\frac{3}{11}$ =1+$\frac{3}{11}$ =$\frac{14}{11}$
c) ($\frac{1}{3}$+$\frac{12}{67}$+ $\frac{13}{41}$)-( $\frac{79}{67}$- $\frac{28}{41}$)=$\frac{1}{3}$+$\frac{12}{67}$+ $\frac{13}{41}$-$\frac{79}{67}$+ $\frac{28}{41}$=$\frac{1}{3}$+( $\frac{12}{67}$- $\frac{79}{67}$)+( $\frac{13}{41}$- $\frac{28}{41}$)= $\frac{1}{3}$ + (-1)+( -$\frac{15}{41}$)= -$\frac{127}{123}$