Giải câu 2 trang 105 toán VNEN 4 tập 2.
a.
$\frac{2}{7} + \frac{4}{7}=\frac{6}{7}$
$\frac{7}{9}- \frac{4}{9}=\frac{5}{9}$
$\frac{2}{5}+\frac{3}{5}=\frac{5}{5}= 1$
b.
$\frac{1}{3}+\frac{5}{12}=\frac{4}{12}+\frac{5}{12}=\frac{9}{12}$
$\frac{7}{12}-\frac{1}{3}=\frac{7}{12}-\frac{4}{12}=\frac{3}{12}$
$\frac{7}{9}-\frac{2}{3}=\frac{7}{9}-\frac{6}{9}=\frac{1}{9}$
c.
$\frac{2}{7}+\frac{4}{5}=\frac{10}{35}+\frac{28}{35}=\frac{38}{35}$
$\frac{2}{3}-\frac{3}{5}=\frac{10}{15}-\frac{9}{15}=\frac{1}{15}$
$\frac{31}{5}-\frac{2}{7}=\frac{217}{35}-\frac{10}{35}=\frac{207}{35}$
d.
$\frac{3}{4}+\frac{1}{6}=\frac{9}{12}+\frac{2}{12}=\frac{21}{12}$
$\frac{11}{12}-\frac{3}{4}=\frac{11}{12}-\frac{9}{12}=\frac{2}{12}$
$\frac{7}{6}-\frac{5}{8}=\frac{28}{24}-\frac{15}{24}=\frac{13}{24}$