(1)105×4-1220×25%,
=420-305,
=115,
答:差是115;
(2)12÷[10×(1-20%)],
=12÷[10×80%],
=12÷8,
=1.5,
答:商是1.5;
(3)设这个数是x,
5x-34×23=72,
5x-782=72,
5x=854,
x=170.8,
答:这个数是170.8.
(1)105×4-1220×25%,
=420-305,
=115,
答:差是115;
(2)12÷[10×(1-20%)],
=12÷[10×80%],
=12÷8,
=1.5,
答:商是1.5;
(3)设这个数是x,
5x-34×23=72,
5x-782=72,
5x=854,
x=170.8,
答:这个数是170.8.