题目内容
20.能简算的要简算.12.5×3.8×0.8 4.4×0.25 2.5×99
2.3×0.9+2.3×9.1 0.25×0.125×4×8 56-2.9×9
17.5-3.25-6.75 9.9×101 3.75-6.8×0.26.
分析 ①根据乘法交换律及结合律计算;
②把4.4写成1.1×4,再根据乘法结合律计算;
③把99写成100-1,再根据乘法分配律计算;
④根据乘法分配律计算;
⑤根据乘法交换律及结合律计算;
⑥先算乘法,再算减法;
⑦根据减法性质进行计算;
⑧把101写成100+1,再根据乘法分配律计算;
⑨先算乘法,再算减法.
解答 解:①12.5×3.8×0.8
=12.5×0.8×3.8
=10×3.8
=38
②4.4×0.25
=1.1×(4×0.25)
=1.1×1
=1.1
③2.5×99
=2.5×(100-1)
=2.5×100-2.5
=250-2.5
=247.5
④2.3×0.9+2.3×9.1
=2.3×(0.9+9.1)
=2.3×10
=23
⑤0.25×0.125×4×8
=(0.25×4)×(0.125×8)
=1×1
=1
⑥56-2.9×9
=56-26.1
=29.9
⑦17.5-3.25-6.75
=17.5-(3.25+6.75)
=17.5-10
=7.5
⑧9.9×101
=9.9×(100+1)
=9.9×100+9.9
=990+9.9
=999.9
⑨3.75-6.8×0.26
=3.75-1.768
=1.982
点评 完成本题要注意分析式中数据,运用合适的简便方法计算.
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