600×10 10×600 0×2000 1×2019×500 20×500 180×40 19×400.
4÷ == %= (写小数)
%= ÷10===0.8.
:4=0.75=9: =.
=3÷ =0.5= :10= %
=9÷ = :16= %= 填小数.