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