4. 计算。
(1)口算。
$40×0.7= $ $8.4÷0.2= $ $1÷4= $ $7.2÷9= $
$3.6×0.2= $ $3.5÷10= $ $9 - 3.8= $ $0.25×8= $
(2)用竖式计算。
$5.07×7.6= $ $4.32÷0.36= $ $19.47×8.3= $
$41.4÷1.8= $ $5.42×2.8= $ $16.8÷3.5= $
(3)计算。
$12.5×4+3.12÷1.2$ $25.2-(7.8 - 2.6)×1.3$

(1)28；42；0.25；0.8；0.72；0.35；5.2；2
(2)

(3)
12.5×4+3.12÷1.2
=50+2.6
=52.6
25.2-(7.8-2.6)×1.3
=25.2-5.2×1.3
=25.2-6.76
=18.44