| 用简便方法计算. (1)5.85+1.89+2.15 (2)24.8+14.6+15.4 (3)42.5-22.17-7.83 (4)3.8+1.37+6.2+12.63. |
| (1)5.85+1.89+2.15 =5.85+2.15+1.89 =8+1.89 =9.89; (2)24.8+14.6+15.4 =24.8+(14.6+15.4) =24.8+30 =54.8; (3)42.5-22.17-7.83 =42.5-(22.17+7.83) =42.5-30 =12.5; (4)3.8+1.37+6.2+12.63 =(3.8+6.2)+(1.37+12.63) =10+14 =24. |
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a.12×(4+25)[ ]
a. 47+(14×5)(1)35+65=
65+35=
35+65○65+35