一、口算。
$\frac{7}{9}+\frac{2}{9}=$ $\frac{9}{20}+\frac{10}{20}=$ $\frac{6}{13}-\frac{1}{13}=$
$\frac{1}{5}+\frac{3}{5}=$ $\frac{13}{24}+\frac{6}{24}=$ $\frac{8}{10}-\frac{5}{10}=$
$\frac{4}{6}-\frac{3}{6}=$ $\frac{14}{5}-\frac{2}{5}=$ $\frac{12}{7}+\frac{5}{7}=$
$\frac{9}{8}-\frac{2}{8}=$ $\frac{8}{17}+\frac{5}{17}=$ $\frac{9}{10}-\frac{4}{10}=$
$\frac{5}{13}+\frac{4}{13}=$ $\frac{10}{8}-\frac{2}{8}=$ $\frac{7}{42}+\frac{34}{42}=$
$\frac{5}{8}-\frac{3}{8}=$ $\frac{2}{11}+\frac{8}{11}=$ $\frac{15}{16}-\frac{3}{16}=$
$\frac{2}{21}+\frac{15}{21}=$ $\frac{10}{9}-\frac{6}{9}=$ $\frac{7}{16}+\frac{5}{16}=$
$\frac{18}{10}-\frac{5}{10}=$ $\frac{3}{4}+\frac{5}{4}=$ $\frac{8}{6}+\frac{4}{6}=$
$\frac{7}{25}+\frac{17}{25}=$ $\frac{11}{12}-\frac{5}{12}=$ $\frac{24}{25}-\frac{8}{25}=$
$\frac{14}{15}-\frac{9}{15}=$ $\frac{25}{33}-\frac{3}{33}=$ $\frac{4}{19}+\frac{6}{19}=$

$\frac{19}{20}$
$\frac{5}{13}$
$\frac{4}{5}$
$\frac{19}{24}$
$\frac{3}{10}$
$\frac{1}{6}$
$\frac{12}{5}$
$\frac{17}{7}$
$\frac{7}{8}$
$\frac{13}{17}$
$\frac{1}{2}$
$\frac{9}{13}$
1
$\frac{41}{42}$
$\frac{1}{4}$
$\frac{10}{11}$
$\frac{3}{4}$
$\frac{17}{21}$
$\frac{4}{9}$
$\frac{3}{4}$
$\frac{13}{10}$
2
2
$\frac{24}{25}$
$\frac{1}{2}$
$\frac{16}{25}$
$\frac{1}{3}$
$\frac{2}{3}$
$\frac{10}{19}$

二、先通分，再比较大小。
$\frac{7}{10}和\frac{8}{15}$ $\frac{6}{7}和\frac{19}{21}$ $\frac{15}{33}和\frac{9}{22}$

$\frac{7}{10}=\frac{21}{30}$ $\frac{8}{15}=\frac{16}{30}$ $\frac{7}{10}＞\frac{8}{15}$
$\frac{6}{7}=\frac{18}{21}$ $\frac{19}{21}=\frac{19}{21}$ $\frac{6}{7}＜\frac{19}{21}$
$\frac{15}{33}=\frac{30}{66}$ $\frac{9}{22}=\frac{27}{66}$ $\frac{15}{33}＞\frac{9}{22}$

二、先通分，再比较大小。
$\frac{8}{19}和\frac{15}{38}$ $\frac{19}{25}和\frac{3}{5}$ $\frac{5}{8}和\frac{7}{12}$

$\frac{8}{19}=\frac{16}{38}$ $\frac{15}{38}=\frac{15}{38}$ $\frac{8}{19}＞\frac{15}{38}$
$\frac{19}{25}=\frac{19}{25}$ $\frac{3}{5}=\frac{15}{25}$ $\frac{19}{25}＞\frac{3}{5}$
$\frac{5}{8}=\frac{15}{24}$ $\frac{7}{12}=\frac{14}{24}$ $\frac{5}{8}＞\frac{7}{12}$