一、口算。
21×40 =
306÷3 =
69 + 31 =
90÷6 =
96 - 28 =
70×70 =
220 - 80 =
204÷2 =
95÷5 =
390 + 30 =
40×22 =
109×3 =
62×6 =
27 + 15 =
729÷9 =
$\frac{3}{4}-\frac{2}{4}=$
$\frac{2}{9}+\frac{5}{9}=$
$\frac{5}{6}-\frac{1}{6}=$
$\frac{4}{23}+\frac{7}{23}=$
$\frac{2}{5}+\frac{2}{5}=$
$\frac{1}{7}+\frac{5}{7}=$
$\frac{7}{10}-\frac{3}{10}=$
$\frac{8}{9}-\frac{4}{9}=$
$\frac{1}{11}+\frac{5}{11}=$
$\frac{7}{8}-\frac{5}{8}=$
$\frac{9}{19}+\frac{13}{19}=$
$\frac{3}{12}-\frac{2}{12}=$
$\frac{5}{14}+\frac{3}{14}=$
$\frac{8}{10}-\frac{5}{10}=$
$\frac{4}{17}+\frac{10}{17}=$

840 102 100
15 68 4900
140 102 19
420 880 327
372 42 81
$\frac{1}{4}$ $\frac{7}{9}$ $\frac{4}{6}$
$\frac{11}{23}$ $\frac{4}{5}$ $\frac{6}{7}$
$\frac{4}{10}$ $\frac{4}{9}$ $\frac{6}{11}$
$\frac{2}{8}$ $\frac{22}{19}$ $\frac{1}{12}$
$\frac{8}{14}$ $\frac{3}{10}$ $\frac{14}{17}$