1. 直接写出得数。
$\frac{1}{3} + \frac{1}{5} =$
$620 + 31 =$
$\frac{9}{20} × 30 =$
$200 × (1 + 0.3) =$
$\frac{1}{4} × \frac{4}{5} =$
$5.61 + 1.8 =$
$4.8 ÷ 40 =$
$6 ÷ (1 - \frac{99}{100}) =$
$0.4 ÷ \frac{8}{15} =$
$75 × 0.01 =$
$0.03 × 0.2 =$
$80 + 80 × 0.1 =$
$1.43 - 1.2 =$
$80 × \frac{3}{16} =$
$\frac{2}{5} + 4.7 =$
$120 - 120 × \frac{1}{8} =$
$0.4 × \frac{1}{2} =$
$4.2 - 2.8 =$
$5.5 - 2.9 =$
$75 × (1 - \frac{1}{25}) =$
$\frac{7}{8} ÷ \frac{7}{9} =$
$0.88 ÷ 0.11 =$
$0.85 ÷ \frac{17}{20} =$
$\frac{5}{12} × 0.36 ÷ \frac{1}{10} =$

$\frac{8}{15}$
$651$
$\frac{27}{2}$
$260$
$\frac{1}{5}$
$7.41$
$0.12$
$600$
$\frac{3}{4}$
$0.75$
$0.006$
$88$
$0.23$
$15$
$5.1$
$105$
$0.2$
$1.4$
$2.6$
$72$
$\frac{9}{8}$
$8$
$1$
$\frac{3}{2}$

2. 计算下面各题，怎样算简便就怎样算。
$(2.4 - 1.1) × 15 - 7.5$
$(5.6 - 0.68 - 0.32) ÷ 2.3$
$9.25 × 9.9 + 0.925$
$6 ÷ \frac{4}{3} + \frac{4}{3} × 6$
$7.2 × ( \frac{5}{8} - \frac{2}{9} + \frac{7}{12} )$
$\frac{9}{20} ÷ [ 1.5 × ( 0.2 + \frac{4}{5} ) ]$

$12$
$2$
$92.5$
$\frac{25}{2}$
$7.1$
$\frac{3}{10}$

一个比例的两个外项的积加上两个内项的积的和是120，其中一个内项是最小的质数，一个外项是最小的合数。请你写出所有符合条件的比例。

$4:2=30:15$
$4:30=2:15$
$15:30=2:4$
$15:2=30:4$