① 单位换算。(每空1分,共12分)
$3.9\ \mathrm{dm}=(\quad)\mathrm{cm}$
$508\ \mathrm{m}=(\quad)\mathrm{cm}$
$40\ \mathrm{cm}=(\quad)\mathrm{m}$
$7.03\ \mathrm{dm}=(\quad)\mathrm{m}$
$3400\ \mathrm{cm}^2=(\quad)\mathrm{m}^2$
$2000\ \mathrm{dm}^2=(\quad)\mathrm{m}^2$
$340\ \mathrm{cm}^2=(\quad)\mathrm{m}^2$
$7.8\ \mathrm{m}^2=(\quad)\mathrm{cm}^2$
$0.25\ \mathrm{dm}^3=(\quad)\mathrm{cm}^3$
$2.5\ \mathrm{cm}^3=(\quad)\mathrm{dm}^3$
$5000\ \mathrm{m}^3=(\quad)\mathrm{dm}^3$
$560\ \mathrm{dm}^3=(\quad)\mathrm{m}^3$

$3.9\ \mathrm{dm}=39\ \mathrm{cm}$
$508\ \mathrm{m}=50800\ \mathrm{cm}$
$40\ \mathrm{cm}=0.4\ \mathrm{m}$
$7.03\ \mathrm{dm}=0.703\ \mathrm{m}$
$3400\ \mathrm{cm}^2=0.34\ \mathrm{m}^2$
$2000\ \mathrm{dm}^2=20\ \mathrm{m}^2$
$340\ \mathrm{cm}^2=0.034\ \mathrm{m}^2$
$7.8\ \mathrm{m}^2=78000\ \mathrm{cm}^2$
$0.25\ \mathrm{dm}^3=250\ \mathrm{cm}^3$
$2.5\ \mathrm{cm}^3=0.0025\ \mathrm{dm}^3$
$5000\ \mathrm{m}^3=5000000\ \mathrm{dm}^3$
$560\ \mathrm{dm}^3=0.56\ \mathrm{m}^3$

② 直接写出得数。(每题1分,共8分)
$6.9+4.5=$
$23×0.4=$
$0.6×1.5=$
$9.72-4.82=$
$80×0.3=$
$2.1-1.9=$
$0.225+0.775=$
$33÷10=$

$6.9+4.5=11.4$
$23×0.4=9.2$
$0.6×1.5=0.9$
$9.72-4.82=4.9$
$80×0.3=24$
$2.1-1.9=0.2$
$0.225+0.775=1$
$33÷10=3.3$

③ 计算。(每题3分,共18分)
$12.5×0.7×0.8$
$35÷(0.35×2)$
$4.6×0.35+4.6×0.65$
$7.28+0.94+2.72+0.06$
$5.83×2+4.27$
$73.5+26.5÷2.5$

$12.5×0.7×0.8=7$
$35÷(0.35×2)=50$
$4.6×0.35+4.6×0.65=4.6$
$7.28+0.94+2.72+0.06=11$
$5.83×2+4.27=15.93$
$73.5+26.5÷2.5=84.1$

④ 解方程。(每题4分,共12分)
$6.9x - 2.4x = 13.5$
$7(x - 1.2) = 4.2$
$5.67 - x = 0.89$

解:$x=3$
解:$x=1.8$
解:$x=4.78$