Câu 1.
a) $\frac{2}{15}$ + $\left( \frac{-5}{24} \right)$ = $\frac{16}{120}$ + $\left( \frac{-25}{120} \right)$ = $\frac{-9}{120}=\frac{-3}{40}$
b) $\frac{-5}{9}$ - $\left( -\frac{7}{27} \right)$ = $\frac{-15}{27}$ - $\left( -\frac{7}{27} \right)$ = $\frac{-8}{27}$
c) $\left( -\frac{7}{12} \right)$+ 0,75 = $\left( -\frac{7}{12} \right)$+ $\frac{3}{4}$ = $\left( -\frac{7}{12} \right)$ + $\frac{9}{12}$ = $\frac{1}{6}$
d) $\left( \frac{-5}{9} \right)$ - 1,25 = $\left( \frac{-5}{9} \right)$ - $\frac{5}{4}$ = $\left( \frac{-20}{36} \right)$ - $\frac{45}{36}$ = $\frac{-65}{36}$
e) 0,34 . $(-\frac{5}{17})$= $\frac{17}{50}$. $(-\frac{5}{17})=\frac{-1}{10}$
g) $\frac{4}{9}$ : $(-\frac{8}{15})$ = $\frac{4}{9}$ . $(-\frac{-15}{8})$= $-\frac{5}{6}$
h) $(1\frac{2}{3})$ : $(2\frac{1}{2})$ = $\frac{5}{3}$ . $\frac{2}{5}$ = $\frac{2}{3}$
i) $\frac{2}{5}$. (-1,25) = $\frac{2}{5}$. $(-\frac{5}{4})$= $-\frac{1}{2}$
k) $(-\frac{3}{5})$. $(\frac{15}{-7})$. $3\frac{1}{9}$ = $\frac{9}{7}$. $\frac{28}{9}$ = 4