一、口算。
$8.4÷0.4 = $
$5×4 = $
$6.7 + 0.33 = $
$12.6 - 0.9 = $
$6.5×0.2 = $
$0.9 + 2.01 = $
$\frac{5}{9} - \frac{1}{6} = $
$\frac{2}{3} + \frac{5}{14} = $
$8.4÷0.4 = $
21
$4.5÷0.9 = $5
$0.5÷(4.2 - 1.7) = $0.2
$5×4 = $
20
$12.5×0.2 = $2.5
$25×3.3×4 = $330
$6.7 + 0.33 = $
7.03
$1.52÷0.08 = $19
$2 - 0.64 - 0.36 = $1
$12.6 - 0.9 = $
11.7
$3.4×0.4 = $1.36
$37.2×99 + 37.2 = $3720
$6.5×0.2 = $
1.3
$0.42÷7 = $0.06
$0.9 + 0.9÷0.3 = $3.9
$0.9 + 2.01 = $
2.91
$2.97÷10 = $0.297
$20.85 - (3.7 + 1.85) = $15.3
$\frac{5}{9} - \frac{1}{6} = $
$\frac{7}{18}$
$\frac{2}{9} + \frac{4}{15} = $$\frac{22}{45}$
$\frac{1}{2} + \frac{1}{3} + \frac{1}{4} = $$\frac{13}{12}$
$\frac{2}{3} + \frac{5}{14} = $
$\frac{43}{42}$
$\frac{5}{7} - \frac{2}{5} = $$\frac{11}{35}$
$\frac{17}{18} - (\frac{1}{2} + \frac{1}{18}) = $$\frac{7}{18}$
答案
21 5 0.2 20 2.5 330 7.03 19 1 11.7 1.36 3720 1.3 0.06 3.9 2.91 0.297 15.3 $\frac{7}{18}$ $\frac{22}{45}$ $\frac{13}{12}$ $\frac{43}{42}$ $\frac{11}{35}$ $\frac{7}{18}$
二、计算长方体和正方体的表面积。

答案
$2.5×2.5×6=37.5(cm^{2})$ $(3.6×4.4+3.6×5.5+4.4×5.5)×2=119.68(cm^{2})$
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