Question

19．簡便計算．

2.5×6.9×4	3.6×1.01	0.99×0.54
12.5×8.8	4.63×3.8+4.63×6.2	67.4×2.66+67.4×1.66

Answer 1

分析 ①根據(jù)乘法交換律及結(jié)合律計算；
②把1.01寫成1+0.01，再根據(jù)乘法分配律進(jìn)行計算；
③把0.99寫成1-0.01，再根據(jù)乘法分配律進(jìn)行計算；
④把8.8寫成8×1.1，再根據(jù)乘法結(jié)合律計算；
⑤根據(jù)乘法分配律進(jìn)行計算；
⑥根據(jù)乘法分配律進(jìn)行計算．

解答 解：①2.5×6.9×4
=（2.5×4）×6.9
=10×6.9
=69

②3.6×1.01                          
=3.6×（1+0.01）
=3.6×1+3.6×0.01
=3.6+0.036
=3.636

③0.99×0.54
=（1-0.01）×0.54
=1×0.54-0.01×0.54
=0.54-0.0054
=0.5356

④12.5×8.8
=12.5×8×1.1
=100×1.1
=110

⑤4.63×3.8+4.63×6.2
=4.63×（3.8+6.2）
=4.63×10
=46.3

⑥67.4×2.66+67.4×1.66
=67.4×（2.66+1.66）
=67.4×4.32
=291.168

點評 完成本題要注意分析式中數(shù)據(jù)，運用合適的簡便方法計算．