Đáp án + Giải thích các bước giải:

a) 3 .  $\frac{-5}{11}$ 

= $\frac{3 . (-5)}{11}$ 

= $\frac{-15}{11}$ 

b) $\frac{3}{5}$ + $\frac{4}{7}$ * $\frac{14}{6}$ 

= $\frac{3}{5}$ + $\frac{4}{3}$ 

= $\frac{9}{15}$ + $\frac{20}{15}$ 

= $\frac{29}{15}$ 

c) $\frac{10}{21}$ - $\frac{3}{8}$ * $\frac{4}{15}$ 

= $\frac{10}{21}$ - $\frac{1}{10}$ 

= $\frac{100}{210}$ - $\frac{21}{210}$ 

= $\frac{79}{210}$ 

d) ( $\frac{2}{3}$ + $\frac{3}{4}$ ) . ( $\frac{5}{7}$ + $\frac{5}{14}$ ) 

= ( $\frac{8}{12}$ + $\frac{9}{12}$ ) . ( $\frac{10}{14}$ + $\frac{5}{14}$ ) 

= $\frac{7}{4}$ . $\frac{15}{14}$ 

= $\frac{15}{8}$