脫式計(jì)算(分能簡算的要簡算.)
70.8-1.25-1.755.81+8.3+4.19+11.78.7×9.9
0.25×17.3×0.40.15×9+0.153.54×0.29-0.29×2.54.

解:
(1)70.8-1.25-1.75,
=70.8-(1.25+1.75),
=70.8-3,
=67.8;

(2)5.81+8.3+4.19+11.7,
=(5.81+4.19)+(8.3+11.7),
=10+20,
=30;

(3)8.7×9.9,
=8.7×(10-0.1),
=8.7×10-8.7×0.1,
=87-0.87,
=86.13;

(4)0.25×17.3×0.4,
=0.25×0.4×17.3,
=0.1×17.3,
=1.73;

(5)0.15×9+0.15,
=0.15×(9+1),
=0.15×10,
=1.5;

(6)3.54×0.29-0.29×2.54,
=(3.54-2.54)×0.29,
=1×0.29,
=0.29.
分析:(1)根據(jù)連減的性質(zhì)進(jìn)行計(jì)算;
(2)根據(jù)加法交換律和結(jié)合律進(jìn)行計(jì)算;
(4)根據(jù)乘法交換律進(jìn)行計(jì)算;
(3)(5)(6)根據(jù)乘法分配律進(jìn)行計(jì)算.
點(diǎn)評:四則運(yùn)算,先弄清運(yùn)算順序,然后再進(jìn)一步計(jì)算,能簡算的要簡算.
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