280×5的积的末尾的 个0,205×4的积的末尾有 个0.
=28: =0.8= ÷10= %= .
=9: = ÷20== %
3:4= :12=12÷ == %
=75÷ =0.75= : = %= 折.
5:8= %;0.25的倒数是 .