Bài 1:
a) $\frac{2}{3}$ + $\frac{5}{6}$
= $\frac{2.2}{3.2}$ + $\frac{5}{6}$
= $\frac{4}{6}$ + $\frac{5}{6}$ = $\frac{9}{6}$ = $\frac{3}{2}$
b) $\frac{1}{4}$ - $\frac{7}{6}$
= $\frac{1.3}{4.3}$ - $\frac{7.2}{6.2}$
= $\frac{3}{12}$ - $\frac{14}{12}$
= $\frac{-11}{12}$
c) $\frac{19}{2}$ - $\frac{5}{6}$
= $\frac{19.3}{2.3}$ - $\frac{5}{6}$
= $\frac{57}{6}$ - $\frac{5}{6}$
= $\frac{52}{6}$ = $\frac{26}{3}$
d) $\frac{2}{3}$ - $\frac{5}{6}$ + $\frac{1}{12}$
= $\frac{8}{12}$ - $\frac{10}{12}$ + $\frac{1}{12}$
= $\frac{-1}{12}$
e) $\frac{3}{4}$ + $\frac{3}{16}$ - $\frac{1}{2}$
= $\frac{12}{16}$ + $\frac{3}{16}$ - $\frac{8}{16}$
= $\frac{7}{16}$
f) $\frac{2}{5}$ - $\frac{4}{7}$ + $\frac{1}{2}$
= $\frac{28}{70}$ - $\frac{40}{70}$ + $\frac{35}{70}$
= $\frac{23}{70}$
Bài 2:
a) A = $\frac{-1}{21}$ + $\frac{-1}{28}$
= $\frac{-4}{84}$ - $\frac{3}{84}$
= $\frac{-7}{84}$ = -$\frac{1}{12}$
Vậy A = $\frac{-1}{12}$
b) B = $\frac{-8}{18}$ - $\frac{15}{27}$
= $\frac{-24}{54}$ - $\frac{30}{54}$
= $\frac{-54}{54}$ = -1
Vậy B = -1
c) C = -$\frac{5}{12}$ + 0,75
= -$\frac{5}{12}$ + $\frac{3}{4}$
= -$\frac{5}{12}$ + $\frac{9}{12}$
= $\frac{4}{12}$ = $\frac{1}{3}$
Vậy C = $\frac{1}{3}$
d) D = 3,5 - (-$\frac{2}{7}$)
= $\frac{7}{2}$ + $\frac{2}{7}$
= $\frac{49}{14}$ + $\frac{4}{14}$
= $\frac{53}{14}$
