1. 直接写出得数。
2.05 - 1.5 =
0.45 × 0.2 =
2.3 × 0.2 =
4.5 + 0.68 - 0.32 =
2.5 ÷ 0.01 =
3.8 - 2.4 =
3.2 + 0.15 =
6.06 ÷ 0.2 × 0.1 =
6.3 ÷ 0.03 =
0.015 ÷ 0.03 =
1.8 × 0.3 =
0.46 ÷ 0.23 × 23 =
$\frac{2}{9} ÷ \frac{4}{7} =$
$\frac{2}{15} × 7.5 =$
$\frac{3}{5} × \frac{4}{15} =$
$( \frac{5}{6} + \frac{1}{4} ) ÷ 0.5 =$
$\frac{9}{8} × \frac{26}{27} =$
$\frac{1}{2} ÷ \frac{1}{7} =$
$\frac{7}{2} ÷ 1.25 =$
$0.36 × 5 - \frac{3}{5} =$
$\frac{5}{9} ÷ \frac{5}{18} =$
$\frac{12}{11} ÷ \frac{1}{4} =$
$\frac{9}{10} + 0.6 =$
$7 ÷ \frac{2}{3} + 4.5 =$

1. 0.55
0.09
0.46
4.86
250
1.4
3.35
3.03
210
0.5
0.54
46
$\frac{7}{18}$
1
$\frac{4}{25}$
$\frac{13}{6}$
$\frac{13}{12}$
$\frac{7}{2}$
$\frac{14}{5}$
1.2
2
$\frac{48}{11}$
1.5
15

2. 计算下面各题,怎样算简便就怎样算。
$10.6 - 1.2 ÷ 0.6 + 3.28$
$0.8 × (4.8 - 2.4) ÷ 0.15$
$3.74 ÷ [4.2 - (1.5 + 0.83)]$
$7 × ( \frac{4}{7} + \frac{5}{8} - \frac{3}{4} ) × 0.8$
$1 - \frac{2}{13} ÷ \frac{8}{13} - \frac{3}{4}$
$[ 2 - ( \frac{6}{5} + \frac{7}{10} ) ] ÷ 1.2$

$10.6 - 1.2 ÷ 0.6 + 3.28$
$= 10.6 - 2 + 3.28$
$= 8.6 + 3.28$
$= 11.88$
$0.8 × (4.8 - 2.4) ÷ 0.15$
$= 0.8 × 2.4 ÷ 0.15$
$= 1.92 ÷ 0.15$
$= 12.8$
$3.74 ÷ [4.2 - (1.5 + 0.83)]$
$= 3.74 ÷ [4.2 - 2.33]$
$= 3.74 ÷ 1.87$
$= 2$
$7 × ( \frac{4}{7} + \frac{5}{8} - \frac{3}{4} ) × 0.8$
$= 7 × 0.8 × \frac{4}{7} + 7 × 0.8 × \frac{5}{8} - 7 × 0.8 × \frac{3}{4}$
$= 3.2 + 3.5 - 4.2$
$= 2.5$
$1 - \frac{2}{13} ÷ \frac{8}{13} - \frac{3}{4}$
$= 1 - \frac{2}{13} × \frac{13}{8} - \frac{3}{4}$
$= 1 - \frac{1}{4} - \frac{3}{4}$
$= 1 - ( \frac{1}{4} + \frac{3}{4} )$
$= 1 - 1$
$= 0$
$[ 2 - ( \frac{6}{5} + \frac{7}{10} ) ] ÷ 1.2$
$= [ 2 - \frac{19}{10} ] ÷ \frac{6}{5}$
$= \frac{1}{10} × \frac{5}{6}$
$= \frac{1}{12}$

验证“除以一个不等于0的数等于乘这个数的倒数”，聪聪的方法是$\frac{7}{16} ÷ \frac{3}{4} = ( \frac{7}{16} × \frac{4}{3} ) ÷ ( \frac{3}{4} × \frac{4}{3} ) = ( \frac{7}{16} × \frac{4}{3} ) ÷ 1 = \frac{7}{16} × \frac{4}{3}$。运用以上方法验证$a ÷ b = a × \frac{1}{b} (b ≠ 0)$。

$a÷ b$
$=(a× \frac{1}{b})÷ (b× \frac{1}{b})$
$=(a× \frac{1}{b})÷ 1$
$=a× \frac{1}{b}\ (b≠0)$