4. 计算。
(1) 口算。
$2.5×4 = $ $7.2÷9 = $ $0.36×0.5 = $ $0.84÷0.2 = $
$0.126÷3 = $ $4.5×3 = $ $1.2×1.1 = $ $0.57÷0.3 = $
(2) 用竖式计算。
$3.28×24.5 = $ $14.4÷0.36 = $
(3) 用简便方法计算。
$0.3×0.25×0.4$ $0.64×1.25$
$0.2×7.185×5$ $5.67×99$

(1)
$2.5×4 = 10$
$7.2÷9 = 0.8$
$0.36×0.5 = 0.18$
$0.84÷0.2 = 4.2$
$0.126÷3 = 0.042$
$4.5×3 = 13.5$
$1.2×1.1 = 1.32$
$0.57÷0.3 = 1.9$
(2)

(3)
$0.3×0.25×0.4$
$=0.3×(0.25×0.4)$
$=0.3×0.1$
$=0.03$
$0.64×1.25$
$=0.8×0.8×1.25$
$=0.8×(0.8×1.25)$
$=0.8×1$
$=0.8$
$0.2×7.185×5$
$=0.2×5×7.185$
$=1×7.185$
$=7.185$
$5.67×99$
$=5.67×(100 - 1)$
$=5.67×100 - 5.67×1$
$=567 - 5.67$
$=561.33$