《2025年口算训练六年级数学下册北师大版升级版》

$3.14×2=$ $3.14×3=$ $3.14×4=$
$3.14×5=$ $3.14×6=$ $3.14×7=$
$3.14×8=$ $3.14×9=$ $3.14×30=$
$3.14×50=$ $3.14×400=$ $3.14×( )=9.42$
$3.14×( )=31.4$ $3.14×( )=21.98$ $3.14×( )=18.84$
$3.14×( )=2826$ $3.14×( )=15.7$ $3.14×( )=251.2$

答案：

计算圆的周长。
$r = 2\text{ cm}$ $C = ( )\text{ cm}$ $d = 2\text{ cm}$ $C = ( )\text{ cm}$
$r = 0.4\text{ m}$ $C = ( )\text{ m}$ $d = 0.4\text{ m}$ $C = ( )\text{ m}$
$r = 3\text{ cm}$ $C = ( )\text{ cm}$ $d = 3\text{ cm}$ $C = ( )\text{ cm}$
$r = 5\text{ dm}$ $C = ( )\text{ dm}$ $d = 5\text{ dm}$ $C = ( )\text{ dm}$
$d = 0.1\text{ dm}$ $C = ( )\text{ dm}$ $d = 200\text{ cm}$ $C = ( )\text{ cm}$
$r = 25\text{ dm}$ $C = ( )\text{ dm}$ $r = 3.5\text{ dm}$ $C = ( )\text{ dm}$
$r = 300\text{ cm}$ $C = ( )\text{ cm}$ $d = 0.06\text{ m}$ $C = ( )\text{ m}$
$r = 15\text{ dm}$ $C = ( )\text{ dm}$ $r = 4.5\text{ cm}$ $C = ( )\text{ cm}$
$d = 0.9\text{ dm}$ $C = ( )\text{ dm}$ $r = 9\text{ cm}$ $C = ( )\text{ cm}$

答案：

一个圆按照$2:1$的比放大，半径扩大到原来的( )倍，直径扩大到原来的( )倍，周长扩大到原来的( )倍，面积扩大到原来的( )倍。

答案：