Question

13．簡便計算：

2.71×6.5+3.5×2.71	0.79×34+7.9×5.6	0.58×9.9
12.5×27.6×0.8	15.52+6.87+4.48+2.13	70.8-4.25-5.75
3.54×0.29-0.29×2.54	48×0.69+3.1×4.8	27.4×10.1

Answer 1

分析 ①③⑦⑨運用乘法分配律的運算．
②根據(jù)積不變規(guī)律特點，把原式改寫成7.9×3.4+7.9×5.6，然后運用乘法分配律的逆運算簡算．
④運用乘法交換律計算．
⑤運用加法交換律和結(jié)合律計算．
⑥運用減法的性質(zhì)計算．
⑧根據(jù)積不變規(guī)律特點，把原式改寫成4.8×6.9+3.1×4.8，然后運用乘法分配律的逆運算簡算．

解答 解：①2.71×6.5+3.5×2.71
=2.71×（6.5+3.5）
=2.71×10
=27.1

②0.79×34+7.9×5.6
=7.9×3.4+7.9×5.6
=7.9×（3.4+5.6）
=7.9×9
=71.1

③0.58×9.9
=0.58×（10-0.1）
=0.58×10-0.58×0.1
=5.8-0.058
=5.742

④12.5×27.6×0.8
=12.5×0.8×27.6
=10×27.6
=276

⑤15.52+6.87+4.48+2.13
=（15.52+4.48）+（6.87+2.13）
=20+9
=29

⑥70.8-4.25-5.75
=70.8-（4.25+5.75）
=70.8-10
=60.8

⑦3.54×0.29-0.29×2.54
=0.29×（3.54-2.54）
=0.29×1
=0.29

⑧48×0.69+3.1×4.8
=4.8×6.9+3.1×4.8
=（6.9+3.1）×4.8
=10×4.8
=48

⑨27.4×10.1
=27.4×（10+0.1）
=27.4×10+27.4×0.1
=274+2.74
=276.74

點評 注意運算法則，靈活運用所學的運算定律簡便計算．