4. 计算。
(1)口算。
$1×0.72 = $ $1.21÷1.1 = $ $5.3×5 = $ $5.6÷4 = $
$4.8 + 2.1 = $ $3.6÷0.6 = $ $1.7×0.5 = $ $7.9÷100 = $
(2)用竖式计算。
$78.6×3.5 = $ $103.6÷37 = $ $8.2×21.3 = $
(3)怎样算简便就怎样算。
$3.28×4.6 + 6.72×4.6$ $0.25×1.25×3.2$
$9.73×2.8 - 4.73×2.8$ $14.08÷[0.8×(7.93 - 2.43)]$

(1)
$1×0.72 = 0.72$
$1.21÷1.1 = 1.1$
$5.3×5 = 26.5$
$5.6÷4 = 1.4$
$4.8 + 2.1 = 6.9$
$3.6÷0.6 = 6$
$1.7×0.5 = 0.85$
$7.9÷100 = 0.079$
(2)
$78.6×3.5 = 275.1$
$\begin{array}{r r r}&&&&7&8.&6 \\ ×&&&&&3.&5 \\ \hline &&3&9&3&0 \\ &2&3&5&8 \\ \hline &2&7&5.&1&0\end{array}$
$103.6÷37 = 2.8$
$\begin{matrix}\:\:\:\:\:\:\:\:2.8\:\:\:\:\:\:\ \\ 37\overline{)103.6}\:\:\:\:\ \\ \:\:\:\:\:\:\underline{74}\:\:\:\:\:\:\:\:\:\:\:\:\ \\ \:\:\:\:\:\:296\:\:\:\:\:\:\:\:\:\ \\ \:\:\:\:\:\:\underline{296}\:\:\:\:\:\:\:\:\:\ \\ \:\:\:\:\:\:\:\:\:\:0\:\:\:\:\:\:\:\:\:\:\end{matrix}$
$8.2×21.3 = 174.66$
$\begin{array}{r r r}&&&&&8.&2 \\ ×&&&2&1.&3 \\ \hline &&&2&4&6 \\ &&8&2 \\ &1&6&4 \\ \hline &1&7&4.&6&6\end{array}$
(3)
$3.28×4.6 + 6.72×4.6$
$=(3.28 + 6.72)×4.6$
$=10×4.6$
$= 46$
$0.25×1.25×3.2$
$=0.25×1.25×0.8×4$
$=(0.25×4)×(1.25×0.8)$
$=1×1$
$= 1$
$9.73×2.8 - 4.73×2.8$
$=(9.73 - 4.73)×2.8$
$=5×2.8$
$= 14$
$14.08÷[0.8×(7.93 - 2.43)]$
$=14.08÷[0.8×5.5]$
$=14.08÷4.4$
$= 3.2$