一、口算。
$0.4^2 - 0.3^2 =$
$1.256 ÷ 3.14 =$
$2 × 3.14 × 0.3 =$
$0.77 + 0.33 =$
$94.2 ÷ 3.14 =$
$157 ÷ 3.14 ÷ 2 =$
$6.4 ÷ 0.8 =$
$3.14 × 500 =$
$3.14 × 20 ÷ 4 =$
$0.9 - 0.26 =$
$3.14 × 0.02 =$
$3.14 × 0.6^2 ÷ 2 =$
$48 × 8 =$
$1570 ÷ 314 =$
$3.14 × (80 ÷ 2)^2 =$
$2.5 × 0.8 =$
$6.28 ÷ 3.14 =$
$3.14 × 6^2 ÷ 4 =$
$0.105 × 100 =$
$3.14 × 70 =$
$3.14 × (10^2 - 6^2) =$
$36 + 12 =$
$75.36 ÷ 3.14 =$
$3.14 × (18 ÷ 2)^2 =$

0.07
0.4
1.884
1.1
30
25
8
1570
15.7
0.64
0.0628
0.5652
384
5
5024
2
2
28.26
10.5
219.8
200.96
48
24
254.34

二、计算下面各图形的周长。
1.
2.

1. $20×2+16+3.14×16÷2=81.12(cm)$
2. $3.14×50×2=314(cm)$

三、计算下面各图形中涂色部分的面积。
1.
2.

1. $3.14×(10÷2)^2÷2-10×(10÷2)÷2=14.25(m^2)$
2. $3.14×2^2÷4=3.14(cm^2)$