3.29+0.73+2.27 3.29-0.73-2.27 =3.29+(0.73+2.27) =3.29-(0.73+2.27) =3.29+3 =3.29-3 =6.29=0.29 (加法结合律)(减法的性质) 7.5+2.5-7.5+2.5 7.325-3.29-3.325 =(7.5-7.5)+(2.5+2.5)=7.325-3.325-3.29 =0+5=4-3.29 =5=0.71 (同级运算交换)(减法交换) 7.325-(5.325+1.7) 7.325-(5.325-1.7) =7.325-5.325-1.7=7.325-5.325+1.7 =2-1.7 =2+1.7 =0.3 =3.7