1. 口算。（建议用时3分钟）
$80\% × \frac{1}{2} =$
$8 × \frac{5}{6} =$
$50 × (1 - 10\%) =$
$\frac{5}{8} - 50\% =$
$60\% × \frac{5}{6} =$
$36 × (1 - 80\%) =$
$\frac{25}{6} ÷ 5 =$
$\frac{4}{7} + \frac{3}{7} =$
$22 ÷ (44\% - 22\%) =$
$\frac{5}{8} - 25\% =$
$\frac{5}{9} × 30\% =$
$100 × 27\% × 2 =$
$\frac{3}{7} ÷ \frac{9}{14} =$
$\frac{1}{2} - \frac{1}{3} =$
$30 × (1 - 79\%) =$
$\frac{7}{4} × 8 =$
$\frac{1}{3} × \frac{1}{7} =$
$80 ÷ (1 - 20\%) =$

$80\% × \frac{1}{2} = 0.4$
$8 × \frac{5}{6} = \frac{20}{3}$
$50 × (1 - 10\%) = 45$
$\frac{5}{8} - 50\% = \frac{1}{8}$
$60\% × \frac{5}{6} = 0.5$
$36 × (1 - 80\%) = 7.2$
$\frac{25}{6} ÷ 5 = \frac{5}{6}$
$\frac{4}{7} + \frac{3}{7} = 1$
$22 ÷ (44\% - 22\%) = 100$
$\frac{5}{8} - 25\% = \frac{3}{8}$
$\frac{5}{9} × 30\% = \frac{1}{6}$
$100 × 27\% × 2 = 54$
$\frac{3}{7} ÷ \frac{9}{14} = \frac{2}{3}$
$\frac{1}{2} - \frac{1}{3} = \frac{1}{6}$
$30 × (1 - 79\%) = 6.3$
$\frac{7}{4} × 8 = 14$
$\frac{1}{3} × \frac{1}{7} = \frac{1}{21}$
$80 ÷ (1 - 20\%) = 100$

2. 计算下面各题，能用简便算法的就用简便算法。（建议用时5分钟）
$160×\frac{3}{4}×40\%$
$800 - 800×2.25\%$
$25\% ×12.5\% ÷\frac{1}{32}$
$\frac{4}{11}÷6 + \frac{7}{11}×\frac{1}{6}$
$12×(1 - \frac{2}{3}÷75\%)$
$25\% ×60÷(1 + 50\%)$

$160×\frac{3}{4}×40\% = 48$
$800 - 800×2.25\% = 782$
$25\% ×12.5\% ÷\frac{1}{32} = 1$
$\frac{4}{11}÷6 + \frac{7}{11}×\frac{1}{6} = \frac{1}{6}$
$12×(1 - \frac{2}{3}÷75\%) = \frac{4}{3}$
$25\% ×60÷(1 + 50\%) = 10$

3. 解决问题。（建议用时2分钟）
请找出下面诗歌中的已知量，解答问题：原计划的听众有多少人？
杏坛讲座韵悠长，雅士纷来聚一堂。当日听众四百二，
竟比原计多两成。原计听众多少位，邀君展卷细思量。

$420÷(1+20\%)=350$(人)