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看谁算得巧妙.
1.29+3.7+0.71+6.38.65÷5×1.38.4÷(0.5+1.6)
0.25×4.5×4×60.85×25-17×0.85(7.9-2.4-3.6)×2.5.

解:(1)1.29+3.7+0.71+6.3,
=(1.29+0.71)+(3.7+6.3),
=2+10,
=12;

(2)8.65÷5×1.3,
=1.73×1.3,
=2.249;

(3)8.4÷(0.5+1.6),
=8.4÷2.1,
=4;

(4)0.25×4.5×4×6,
=(0.25×4)×(4.5×6),
=1×27,
=27;

(5)0.85×25-17×0.85,
=0.85×(25-17),
=0.85×8,
=6.8;

(6)(7.9-2.4-3.6)×2.5,
=[7.9-(2.4+3.6)]×2.5,
=[7.9-6]×2.5,
=1.9×2.5,
=4.75.
分析:(1)根据加法交换律和结合律进行简算;
(2)先算除法,再算乘法;
(3)先计算括号里面的加法,再计算除法;
(4)根据乘法交换律和结合律进行简算;
(5)根据乘法分配律进行简算;
(6)括号里面的7.9连续减去2.4与3.6,等于减去2.4与3.6的和,最后再计算乘法.
点评:小数的四则混合运算,先找清运算顺序,然后再进一步计算,能简算的要简算.
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看谁算得巧妙.
1.29+3.7+0.71+6.3 8.65÷5×1.3 8.4÷(0.5+1.6)
0.25×4.5×4×6 0.85×25-17×0.85 (7.9-2.4-3.6)×2.5.

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