并合律25×(40-4)=25×40-25×4=1000-100=90025x(40-4)= 25×40-25×4 = 1000-100 = 90025x(40-4)= 25x 40-25x 4 = 1000-100 = 900谢谢，请收下。原公式=25*40-25*4=1000-100=900
