7.2x0.25 +2.8÷4＝7.2x1/4 +2.8÷4＝7.2÷4 +2.8÷4＝（7.2 +2.8）÷4＝10÷4 ＝2.5
原式=7.2÷4+2.8÷4=（7.2+2.8）÷4=10÷4=2.5
原式=7.2*(1/4)+2.8*(1/4)=(1/4)*(7.2+2.8)=(1/4)*10=5/2
