一、口算。
$3.9÷1.3=$ $0.8×5.2=$ $4.9÷0.98=$
$0.04×0.3=$ $0.9+1.4=$ $4.2-0.42=$
$0.6×8=$ $10÷0.25=$ $8×1.25=$
$1.6÷0.04=$ $1.8×5=$ $36÷30=$
$4×1.65=$ $1.23+0.87=$ $0.89-0.25=$
$50÷0.5=$ $4.8+5.2=$ $0.35×20=$
$\frac {4}{5}+\frac {1}{4}=$ $\frac {1}{3}-\frac {1}{4}=$ $\frac {3}{4}+\frac {1}{6}=$
$\frac {5}{8}-\frac {7}{12}=$ $\frac {7}{20}-\frac {1}{5}=$ $\frac {1}{3}+\frac {5}{12}=$

$3.9÷1.3=3$
$0.8×5.2=4.16$
$4.9÷0.98=5$
$0.04×0.3=0.012$
$0.9+1.4=2.3$
$4.2-0.42=3.78$
$0.6×8=4.8$
$10÷0.25=40$
$8×1.25=10$
$1.6÷0.04=40$
$1.8×5=9$
$36÷30=1.2$
$4×1.65=6.6$
$1.23+0.87=2.1$
$0.89-0.25=0.64$
$50÷0.5=100$
$4.8+5.2=10$
$0.35×20=7$
$\frac{4}{5}+\frac{1}{4}=\frac{21}{20}$
$\frac{1}{3}-\frac{1}{4}=\frac{1}{12}$
$\frac{3}{4}+\frac{1}{6}=\frac{11}{12}$
$\frac{5}{8}-\frac{7}{12}=\frac{1}{24}$
$\frac{7}{20}-\frac{1}{5}=\frac{3}{20}$
$\frac{1}{3}+\frac{5}{12}=\frac{3}{4}$

 

二、计算下面各图形的体积。

5×5×1+3×3×3=52(cm³)
25×15×20-(25-15)×15×(20-10)=6000(cm³)