《小学数学五级上册小数乘法的简便运算课件.pptx

Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 看谁算得快 0.32×100 24＋0.24 15－0.15 0.4×0.5 1.25×8 2.5×4 0.24×5 0.6×0.1 = 32 = 24.24 = 14.85 = 0.2 = 10 = 10 = 1.2 = 0.06 0.5×0.2= 50×0.2= 500×0.2= 0.1 10 100 2.5×0.4 = 1 0.25×40 = 10 1.25×0.8 = 1 1.25×80 = 100 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 2、在括号里填上适当的数。 (1)0.32=4×( ) (2)1.02=1+( ) (3)0.99=1-( ) (4)9.8=( )-( ) 0.08 10 0.01 0.02 0.2 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 看谁算得巧 (23×4)×15 25×73×4 102×32 = 25×4×73 = 100×73 = 7300 = 23×(4×15) = 23×60 = 1380 = (100+2)×32 = 100×32+2×32 = 3200+64 = 3264 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 3、思考：乘法有哪些运算定律？ 怎样用字母式子表示？ 乘法交换律： a×b=b×a 乘法结合律： (a×b) ×c=a× (b×c) 乘法分配律： (a+b) ×c=a×c+b×c Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 观察下面每组的两个算式，它们有什么关系？ = = = 整数乘法的交换律、结合律和分配律，对于小数乘法同样适用。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. ＝1×4.78   ＝4.78   0.25×4.78×4  0.65×201 ＝130＋0.65 ＝130.65 ＝0.25×4×4.78 ＝0.65×（200＋1） ＝0.65×200＋0.65 例8 根据乘法交换律 乘法分配律 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 小数简便计算计算应注意的问题： 一审： 审清题目。 二看： 观察数字特征，选择合理的运算定律。 三算： 认真计算。 四查： 查运算顺序；查数字；查每一步的计算。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 　4.2×1.69＝ ×  2.5×0.77×0.4＝（ × ）× 6.1×3.6+3.9×3.6＝（ ＋ ）× 1.69 4.2 2.5 0.4 0.77 6.1 3.9 3.6 Evaluation only. Cre