五年级奥数专题解小 例题】 例1 用简便方法计算下面各题. (1)(4.8×7.5×8.1)÷(2.4×2.5×2.7) 解：(1)解法一： (4.8×7.5×8.1)÷(2.4×2.5×2.7) =(48×75×81)÷(24×25×27) =(12×4×25×3×81)÷(6×4×25×3×9) =(12×100×3×81)÷(6×100×3×9) =(12×81)÷(6×9) =(2×6×9×9)÷(6×9) =2×9=18 解法二： (4.8×7.5×8.1)÷(2.4×2.5×2.7) =(4.8÷2.4)×(7.5÷2.5)×(8.1÷2.7) =2×3×3=18 (2)0.125×0.25×0.5×64 解法一： 0.125×0.25×0.5×64 =0.125×0.25×0.5×(2×4×8) =(0.125×8)×(0.25×4)×(0.5×2) =1×1×1=1 解法二： 0.125×0.25×0.5×64 =0.125×(0.25×0.5)×(8×8) =(0.125×8)×(0.125×8) 数四则混合运算简算 =1×1=1 解法三： 0.125×0.25×0.5×64 =(64×0.5)×0.25×0.125 =32×(0.5×0.5)×(0.5×0.5×0.5) =(32×0.5)×0.5×0.5×0.5×0.5 =(16×0.5)×0.5×0.5×0.5 =(8×0.5)×0.5×0.5 =(4×0.5)×0.5 =2×0.5=1 通过第(2)题三种算法，你认为哪一种最简便？你还有没有其它的简便解法？ (3)3.75×4.8＋62.5×0.48 解法一： 3.75×4.8＋62.5×0.48 = 37.5×0.48＋62.5×0.48 =(37.5＋62.5)×0.48 =100×0.48=48 解法二： 3.75×4.8＋62.5×0.48 =3.75×4.8＋6.25×4.8 =(3.75＋6.25)×4.8 =10×4.8=48 (4)1.35×0.61－0.35×0.61 =(1.35－0.35)×0.61 =1×0.61 =0.61 例2 看一看下面的算式有什么特点？运用什么运算定律可以使计算简便？ (1)1.56×1.7＋0.44×1.7－0.7 (2)11.72－7.85－(2.26＋0.46) 解：(1)1.56×1.7＋0.44×1.7－0.7 =1.7×(1.56＋0.44)－0.7 =1.7×2－0.7 =3.4－0.7 =2.7 (2)11.72－7.85－(2.26＋0.46) =11.72－7.85－2.72 =11.72－2.72－7.85 =9－7.85 =1.15 例3 计算：0.1＋0.3＋0.5＋0.7＋…＋0.97＋0.99 分析：从0.1到0.9，前后两个数相差0.2，从0.11到0.99前后两个数相差0.02. 解：0.1＋0.3＋0.5＋0.7＋…＋0.97＋0.99 =(0.1＋0.3＋0.5＋0.7＋0.9)＋(0.11＋0.13＋… ＋0.19)＋(0.21＋0.23＋…＋0.29)＋…＋(0.91 ＋0.93＋…＋0.99) =2.5＋(0.1×5＋0.25)＋(0.25×5＋0.25)＋… ＋(0.9×5＋0.25) =2.5＋(0.1＋0.2＋…＋0.9)×5＋0.25×9 =2.5＋22.5＋2.25=27.25 【练习】 1、用简便方法计算下面各题. (1)5.5×17.3＋6.7×5.5 (2)13.7×0.25×8 (3)32.8＋5.6＋7.2 (4)4.6×2.5×40 (5)12.5×3×3×8 (6)50×0.47×0.2 (7)101×7. (8)10.1×54 (9)42.6－2.77－7.23 (10)16.4－16.4×0.5 (11)2.18＋4.65＋7.82＋4.35 (12)12.48－2.72－3.28 (13)(250＋2.5)×4 (14)4×7×0.5×3×5 (15)(125＋1.25)×8 (16)775＋10.9＋9.1＋225 (17)12.4－2.68－7. (18)7×1.785＋3×1.785 (19)5.25÷15＋3.75÷15 (20)18.4×1.7＋18.4×8.3 (21)7.6×5.3＋7.6×3.7＋7.6 (22)45.6÷38－7.6÷38 (23)(0.45＋0.06＋1.5)÷0.15 (24)2.75÷54＋2. 65÷54 (25)1.25×8.8 (26)0.89×10.1 (27)25×5.26×40 (28)0.125×32×25 (29)0.36×0.5＋0.36×0.4＋0.36×0.1 (30)0.38＋13.4＋1.62＋4.6 (31)0.125×78×80 (32)9.1×1.1－9.1×0.1 (33)0.125×32×25×58 本文来源：https://www.wddqw.com/doc/aff14127a5e9856a561260cb.html