第一类 ①2.27+0.73+2.27 =2.27+(0.73+2.27) =2.27+3 =5.27 ②2.35+5.18+4.82 =2.35+(5.18+4.82) =2.35+10 =12.35 ③1.29+3.7+2.71+6.3 =(1.29+2.71)+(3.7+6.3) =4+10 =14 ④2.64+8.67+7.36+11.33 =(2.64+7.36)+(8.67+11.33) =10+20 =30 第二类 ①3.25-0.73-2.27 =3.25-(0.73+2.27) =3.25-3 =0.25 ②23.15-4.75-3.25 =23.15-(6.75+3.25) =23.15-01 =13.15
