一、口算。
20×63 =
47 + 153 =
720÷4 =
40×90 =
6×400 =
19×50 =
35 + 20 =
270÷9 =
400 - 17 =
380÷2 =
50×64 =
66÷3 =
30×61 =
70 - 18 =
43×30 =
$\frac{3}{11}+\frac{7}{11}=$
$\frac{4}{5}-\frac{1}{5}=$
$\frac{1}{10}+\frac{3}{10}=$
$\frac{5}{9}+\frac{1}{9}=$
$\frac{5}{8}+\frac{2}{8}=$
$\frac{3}{4}-\frac{3}{4}=$
$\frac{17}{28}-\frac{6}{28}=$
$\frac{7}{13}-\frac{5}{13}=$
$\frac{9}{10}-\frac{3}{10}=$
$\frac{8}{17}-\frac{4}{17}=$
$\frac{3}{12}+\frac{4}{12}=$
$\frac{13}{25}+\frac{7}{25}=$
$\frac{5}{19}+\frac{4}{19}=$
$\frac{25}{36}-\frac{13}{36}=$
$\frac{19}{24}-\frac{5}{24}=$

1260 200 180
3600 2400 950
55 30 383
190 3200 22
1830 52 1290
$\frac{10}{11}$ $\frac{3}{5}$ $\frac{4}{10}$
$\frac{6}{9}$ $\frac{7}{8}$ 0
$\frac{11}{28}$ $\frac{2}{13}$ $\frac{6}{10}$
$\frac{4}{17}$ $\frac{7}{12}$ $\frac{20}{25}$
$\frac{9}{19}$ $\frac{12}{36}$ $\frac{14}{24}$

二、计算下面各题。
(505 - 289)÷6
52×(76 - 48)
380÷5×43

36 1456 3268