11.3*2.5-1.3*25 =(10+1.3)*2.5-1.3*25 =25+1.3*2.5-1.3*25 =25(1-1.3)+1.3*2.5 =-3*2.5+1.3*2.5 =2.5(-3+1.3) =2.5*-1.7 =2.5*(0.3-2) =0.75-5 =-4.25 大致就是这个样子~