Question

13．简便计算：

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运用乘法分配律的运算．
②根据积不变规律特点，把原式改写成7.9×3.4+7.9×5.6，然后运用乘法分配律的逆运算简算．
④运用乘法交换律计算．
⑤运用加法交换律和结合律计算．
⑥运用减法的性质计算．
⑧根据积不变规律特点，把原式改写成4.8×6.9+3.1×4.8，然后运用乘法分配律的逆运算简算．

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

点评 注意运算法则，灵活运用所学的运算定律简便计算．