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21.73+(7.02-1.73)+1.98       312-12×16+2440-4.72+5.28           
57×39-39+39×449000÷36             30-[17.8+(6.2+38÷10)].

解:(1)21.73+(7.02-1.73)+1.98,
=(21.73-1.73)+(1.98+7.02),
=20+9,
=29;

(2)312-12×16+24,
=312-192+24,
=120+24,
=144;

(3)40-4.72+5.28,
=35.28+5.28,
=40.56;

(4)57×39-39+39×44,
=(57-1+44)×39,
=100×39,
=3900;

(5)9000÷36,
=(9000÷9)÷(36÷9),
=1000÷4,
=250;

(6)30-[17.8+(6.2+38÷10)],
=30-[17.8+(6.2+3.8)],
=30-[17.8+10],
=30-27.8,
=2.2.
分析:(1)运用加法结合律简算;
(2)先算乘法,再算减法,最后算加法;
(3)按从左到右顺序计算;
(4)运用乘法分配律简算;
(5)根据商不变规律把被除数和除数同时除以9,然后再计算;
(6)先算小括号里面除法,再算小括号里面的加法,然后算中括号里面的加法,最后算括号外的减法.
点评:考查了运算定律与简便运算,四则混合运算.注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
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