学校买来a个足球,每个m元,又买来b个排球,每个n元,一共用去( )元,足球比排球多用( )元.
:20=0.8=12÷ == %= (填成数)
= %= : = (小数)
: =37.5%== ÷ = (填小数)
=0.75== : = %
= : =75%=3÷ = .(填小数)