Question

20．簡便計(jì)算

0.25×0.73×4	（1.25-0.125）×8	3.65×10.1
0.85×99	3.72×3.5+6.28×3.5	4.8×7.8+78×0.52

Answer 1

分析 ①運(yùn)用乘法交換律和結(jié)合律計(jì)算．
②③④⑤⑥運(yùn)用乘法分配律．

解答 解：①0.25×0.73×4
=0.25×4×0.73
=1×0.73
=0.73

②（1.25-0.125）×8
=1.25×8-0.125×8
=10-1
=9

③3.65×10.1
=3.65×（10+0.1）
=3.65×10+3.65×0.1
=36.5+0.365
=36.865

④0.85×99
=0.85×（100-1）
=0.85×100-0.85×1
=85-0.85
=84.15

⑤3.72×3.5+6.28×3.5
=（3.72+6.28）×3.5
=10×3.5
=35

⑥4.8×7.8+78×0.52
=4.8×7.8+7.8×5.2
=（4.8+5.2）×7.8
=10×7.8
=78

點(diǎn)評 此題考查的目的是理解掌握乘法交換律、結(jié)合律、分配律的意義，并且能夠靈活運(yùn)用乘法的這些運(yùn)算定律進(jìn)行簡便計(jì)算．