1. 直接写出得数。
2.8 + 7.2 =
3.1 × 20 =
4.2 ÷ 8 =
0.32 + 0.5 + 0.7 =
0.2 ÷ 5 =
0.4 + 1.3 =
9.02 + 3.9 =
0.96 ÷ 48 ÷ 10 =
0.15 × 40 =
0.24 ÷ 8 =
15 ÷ 2 =
2.5 × 10 - 8 =
32 ÷ 80 =
3.5 × 7 =
10.8 ÷ 9 =
83 ÷ 20 - 0.4 =
0.45 × 6 =
6.06 ÷ 3 =
1.34 - 0.8 =
0.45 ÷ 5 × 2 =
9.3 - 3.9 =
4.28 - 0.8 =
1.3 × 70 =
7.6 - 7.6 + 2.9 =
8.8 ÷ 11 =
8.2 + 0.53 =
4.92 ÷ 4 =
18.5 × 10 ÷ 5 =
4.53 + 2.01 =
0.55 ÷ 5 =
6.8 × 50 =
0.125 × 8 × 10 =

1. 10 62 0.525 1.52
0.04 1.7 12.92 0.002
6 0.03 7.5 17
0.4 24.5 1.2 3.75
2.7 2.02 0.54 0.18
5.4 3.48 91 2.9
0.8 8.73 1.23 37
6.54 0.11 340 10

2. 用简便方法计算。
$359 + 187 + 241$
$720 ÷ 48$
$17 × 56 + 56 × 83$
$137 - 26 + 163 - 74$
$99 × 85$
$125 × (7 × 8)$

2. 787 15 5600
200 8415 7000

如图，边长分别为20厘米和30厘米的两个正方形并排放在一起，求三角形ABC（涂色部分）的面积。

20×30÷2=300(平方厘米)
300×2÷(20+30)=12(厘米)
12×30÷2=180(平方厘米)