a) $\frac{2}{5}$ . $\frac{3}{4}$ : $\frac{6}{11}$
= $\frac{2}{5}$ . $\frac{3}{4}$ . $\frac{11}{6}$
= $\frac{2. 3 . 11 }{5 . 4. 6}$
=$\frac{66}{120}$ = $\frac{11}{20}$
b) $\frac{2}{7}$ - $\frac{3}{8}$
= $\frac{16 - 21}{56}$
= $\frac{-5}{56}$
c) $\frac{5}{4}$ + $\frac{5}{6}$ + $\frac{1}{2}$
= $\frac{15 + 10 + 6}{12}$
= $\frac{31}{12}$
d) $\frac{4}{7}$ : $\frac{2}{3}$ : $\frac{3}{4}$
= $\frac{4}{7}$ . $\frac{3}{2}$ . $\frac{4}{3}$
= $\frac{4 . 3. 4}{7. 2. 3}$
= $\frac{8}{7}$
cho mik xin 5* và ctlhn
@chúc bn hok tốt