《2025年口算训练宁波出版社六年级数学上册人教版》

1. 口算。
$\frac{8}{9} × \frac{3}{4} = $
$0 × \frac{43}{59} = $
$1 ÷ \frac{8}{3} = $
$\frac{4}{7} ÷ 8 = $
$\frac{5}{6} - \frac{3}{10} = $
$\frac{5}{14} ÷ \frac{4}{7} = $
$\frac{7}{8} × \frac{3}{14} = $
$9 ÷ \frac{3}{5} = $
$\frac{2}{11} ÷ \frac{11}{5} = $
$6 × \frac{2}{3} = $
$\frac{4}{15} + \frac{2}{5} = $
$\frac{2}{9} ÷ \frac{1}{3} = $
$\frac{1}{6} × \frac{3}{5} = $

答案： $\frac{2}{3}$
$0$
$\frac{3}{8}$
$\frac{1}{14}$
$\frac{8}{15}$
$\frac{5}{8}$
$\frac{3}{16}$
$15$
$\frac{10}{121}$
$4$
$\frac{2}{3}$
$\frac{2}{3}$
$\frac{1}{10}$

2. 填空。
(1)$r = 3\ \text{cm}$
$C = ($18.84$)\ \text{cm}$
(2)$r = 2\ \text{dm}$
$C = ($12.56$)\ \text{dm}$
$S = ($12.56$)\ \text{dm}^2$
(3)$d = 7\ \text{m}$
$C = ($21.98$)\ \text{m}$
$S = ($38.465$)\ \text{m}^2$
(4)$d = 4\ \text{cm}$
$C = ($12.56$)\ \text{cm}$
$S = ($12.56$)\ \text{cm}^2$
(5)$r = 5\ \text{m}$
$C = ($31.4$)\ \text{m}$
$S = ($78.5$)\ \text{m}^2$
(6)$d = 2\ \text{cm}$
$C = ($6.28$)\ \text{cm}$
$S = ($3.14$)\ \text{cm}^2$
(7)$d = 20\ \text{cm}$
$C = ($62.8$)\ \text{cm}$
$S = ($314$)\ \text{cm}^2$

答案： 解析：
本题主要考查圆的周长和面积的计算。
(1) 已知半径 $r = 3\text{cm}$，则圆的周长 $C = 2\pi r = 2\pi × 3 = 6\pi \approx 18.84\text{cm}$。
(2) 已知半径 $r = 2\text{dm}$，则圆的周长 $C = 2\pi r = 2\pi × 2 = 4\pi \approx 12.56\text{dm}$，面积 $S = \pi r^2 = \pi × 2^2 = 4\pi \approx 12.56\text{dm}^2$。
(3) 已知直径 $d = 7\text{m}$，则半径 $r = \frac{d}{2} = 3.5\text{m}$，圆的周长 $C = \pi d = \pi × 7 = 7\pi \approx 21.98\text{m}$，面积 $S = \pi r^2 = \pi × (3.5)^2 = 12.25\pi \approx 38.465\text{m}^2$。
(4) 已知直径 $d = 4\text{cm}$，则半径 $r = \frac{d}{2} = 2\text{cm}$，圆的周长 $C = \pi d = \pi × 4 = 4\pi \approx 12.56\text{cm}$，面积 $S = \pi r^2 = \pi × 2^2 = 4\pi \approx 12.56\text{cm}^2$。
(5) 已知半径 $r = 5\text{m}$，则圆的周长 $C = 2\pi r = 2\pi × 5 = 10\pi \approx 31.4\text{m}$，面积 $S = \pi r^2 = \pi × 5^2 = 25\pi \approx 78.5\text{m}^2$。
(6) 已知直径 $d = 2\text{cm}$，则半径 $r = \frac{d}{2} = 1\text{cm}$，圆的周长 $C = \pi d = \pi × 2 = 2\pi \approx 6.28\text{cm}$，面积 $S = \pi r^2 = \pi × 1^2 = \pi \approx 3.14\text{cm}^2$。
(7) 已知直径 $d = 20\text{cm}$，则半径 $r = \frac{d}{2} = 10\text{cm}$，圆的周长 $C = \pi d = \pi × 20 = 20\pi \approx 62.8\text{cm}$，面积 $S = \pi r^2 = \pi × 10^2 = 100\pi \approx 314\text{cm}^2$。
答案：
(1) $18.84\text{cm}$
(2) $12.56\text{dm}$；$12.56\text{dm}^2$
(3) $21.98\text{m}$；$38.465\text{m}^2$
(4) $12.56\text{cm}$；$12.56\text{cm}^2$
(5) $31.4\text{m}$；$78.5\text{m}^2$
(6) $6.28\text{cm}$；$3.14\text{cm}^2$
(7) $62.8\text{cm}$；$314\text{cm}^2$