一、口算。
$\frac{12}{9}+\frac{7}{9}=$ $\frac{4}{5}-\frac{3}{5}=$ $\frac{5}{13}+\frac{4}{13}=$
$\frac{15}{10}-\frac{6}{10}=$ $\frac{2}{14}+\frac{6}{14}=$ $\frac{9}{5}-\frac{2}{5}=$
$\frac{2}{7}+\frac{9}{7}=$ $\frac{18}{33}-\frac{5}{33}=$ $\frac{3}{16}+\frac{5}{16}=$
$0.84÷0.7=$ $4.5×0.4=$ $0.31+0.9=$
$200×0.37=$ $0.83-0.62=$ $10.2÷0.6=$
$5.1+3.9=$ $0.63÷9=$ $1.8×30=$
$0.34×0.2=$ $6-0.6=$ $0.9÷1.5=$
$12.5-2.5=$ $4.9÷0.07=$ $1.72+0.3=$
$2.25×4=$ $7.52+0.68=$ $5.6-4.8=$
$0.88+1.2=$ $4-0.25=$ $4.8×0.2=$

$\frac{19}{9}$ $\frac{1}{5}$ $\frac{9}{13}$
$\frac{9}{10}$ $\frac{4}{7}$ $\frac{7}{5}$
$\frac{11}{7}$ $\frac{13}{33}$ $\frac{1}{2}$
$1.2$ $1.8$ $1.21$
$74$ $0.21$ $17$
$9$ $0.07$ $54$
$0.068$ $5.4$ $0.6$
$10$ $70$ $2.02$
$9$ $8.2$ $0.8$
$2.08$ $3.75$ $0.96$

二、通分。
$\frac{13}{28}$和$\frac{9}{14}$ $\frac{14}{15}$和$\frac{7}{9}$ $\frac{3}{4}$和$\frac{13}{18}$

$\frac{13}{28}=\frac{13}{28}$ $\frac{9}{14}=\frac{18}{28}$
$\frac{14}{15}=\frac{42}{45}$ $\frac{7}{9}=\frac{35}{45}$
$\frac{3}{4}=\frac{27}{36}$ $\frac{13}{18}=\frac{26}{36}$