Câu 1:
a. $\frac{5}{7}$ + $\frac{1}{4}$ = $\frac{20}{28}$ + $\frac{7}{28}$ = $\frac{27}{28}$
b. $\frac{-3}{7}$.$\frac{-4}{7}$ = $\frac{12}{49}$
c. $\frac{3}{8}$ - $\frac{-5}{4}$ = $\frac{3}{8}$ + $\frac{10}{8}$ = $\frac{13}{8}$
d. $\frac{1}{4}$ : $\frac{-3}{2}$ = $\frac{1}{4}$.$\frac{-2}{3}$ = $\frac{1}{2}$.$\frac{-1}{3}$ = $\frac{-1}{6}$
e. $\frac{8}{7}$.$\frac{1}{14}$ = $\frac{4}{7}$.$\frac{1}{7}$ = $\frac{4}{49}$
f. $\frac{7}{5}$ + $\frac{6}{7}$ = $\frac{49}{35}$ + $\frac{30}{35}$ = $\frac{79}{35}$
g. $\frac{3}{8}$ : $\frac{-5}{4}$ = $\frac{3}{8}$.$\frac{-4}{5}$ = $\frac{3}{2}$.$\frac{-1}{5}$ = $\frac{-3}{10}$
h. $\frac{-2}{3}$ - $\frac{4}{8}$ = $\frac{-2}{3}$ + $\frac{-1}{2}$ = $\frac{-2}{6}$ + $\frac{-3}{6}$ = $\frac{-5}{6}$
Câu 2:
a. x + $\frac{8}{3}$ = $\frac{7}{3}$
x = $\frac{7}{3}$ - $\frac{8}{3}$
x = $\frac{-1}{3}$
b. $\frac{7}{2}$.x = $\frac{9}{4}$
x = $\frac{9}{4}$ : $\frac{7}{2}$
x = $\frac{9}{4}$.$\frac{2}{7}$
x = $\frac{9}{2}$.$\frac{1}{7}$
x = $\frac{9}{14}$
c. x - $\frac{17}{15}$ = $\frac{-7}{15}$
x = $\frac{-7}{15}$ + $\frac{17}{15}$
x = $\frac{2}{3}$
d. $\frac{9}{2}$ : x = $\frac{-3}{4}$
x = $\frac{9}{2}$ : $\frac{-3}{4}$
x = $\frac{9}{2}$.$\frac{-4}{3}$
x = $\frac{3}{1}$.$\frac{-2}{1}$
x = -6
