一、口算。
3.14×3= 0.77+0.07= 0.6×0.7=
3.14×4= 1.2×0.4= 8.1÷0.09=
3.14×5= 5.7÷30= 3.95+0.5=
3.14×6= 0.14÷0.07= 3.25×4=
3.14×8= 9.9−8.88= 6.8×0.03=
3.14×9= 305×0.2= 5−3.68=
3.14×10= 5×0.58= 0.96÷0.16=
3.14×20= 10÷0.125= 6.4×0.05=
3.14×50= 36.9÷0.03= 7.5×30=
3.14×80= 18−8.36= 8.4×0.04=

$9.42$
$0.84$
$0.42$
$12.56$
$0.48$
$90$
$15.7$
$0.19$
$4.45$
$18.84$
$2$
$13$
$25.12$
$1.02$
$0.204$
$28.26$
$61$
$1.32$
$31.4$
$2.9$
$6$
$62.8$
$80$
$0.32$
$157$
$1230$
$225$
$251.2$
$9.64$
$0.336$

二、计算下面各图形的周长。
1.
2.

1. $2×3.14×2=12.56(\mathrm{dm})$
2. $3.14×3=9.42(\mathrm{cm})$