小数四则混合运算2.ppt

小数四则混合运算（二） 乘法运算定律的推广,学习目标,1. 清楚整数乘法的运算方法及运算定律对于小数乘法同样适用。 2. 提高大家对知识的迁移能力。 3. 提高同学们灵活运用乘法交换律、乘法结合律、乘法分配律解决问题的能力。,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,复习旧知,怎样简便怎样算,25×72×4 36×125×8 35×64+36×35 66×101,=25×4×72,=100×72,=7200,=36×（125×8）,=36×1000,=36000,=35×（64+36）,=35×100,=3500,=66×（100+1）,=66×100+66×1,=6666,=6600+66,0.7×1.21.2×0.7,（0.8×0.5）×0.40.8×（0.5×0.4）,（2.43.6）×0.52.4×0.53.6×0.5,探究新知,仔细观察每一组算式，你发现了什么？,0.7×1.21.2×0.7,（0.8×0.5）×0.40.8×（0.5×0.4）,（2.43.6）×0.52.4×0.53.6×0.5,乘法交换律,乘法结合律,乘法分配律,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。,=0.25×4×4.78,0.25×4.78×4,同学们仔细思考，怎样计算简便呢？,乘法交换律,=1×4.78,=4.78,0.65×201,同学们仔细思考，怎样计算简便呢？,=0.65×2000.65×1,乘法分配律,=0.65×（2001）,=130.65,16×1.25,同学们开动脑筋，怎样算合理简便呢？看谁想的方法最多。,16×1.25,同学们开动脑筋，怎样算合理简便呢？看谁想的方法最多。,16×1.25 =(10+6)×1.25 =10×1.25+6×1.25 =12.5+7.5 =20,16×1.25,同学们开动脑筋，怎样算合理简便呢？看谁想的方法最多。,16×1.25 =(2×8)×1.25 =2×（8×1.25） =2×10 =20,16×1.25,同学们开动脑筋，怎样算合理简便呢？看谁想的方法最多。,= (20-4)×1.25 =20×1.25-4×1.25 =25-5 =20,检测一下自己吧,一、我会填。,2.5×(0.77×0.4)= × ×,7.2×8.4+2.8×8.4=( + )×,2.02×8.5= （ + ）×8.5 ×8.5+ ×8.5,4.2×1.69= ×,0.4,2.5,2,8.4,2.8,7.2,4.2,1.69,0.02,2,0.02,二、我是聪明的小法官。,（1）98×6.5 =(100-2)×6.5 =100×6.5-2×6.5 =637,(2) 12.5×2.5×3.2 =12.5×2.5×(8×0.4) =12.5×8×2.5×0.4 =100×1 =100,一、火眼金睛,(2) 12.5×2.5×3.2 =12.5×2.5×(8×0.4) =12.5×8+2.5×0.4 =100+1 =101,（1）98×6.5 =(98+2)×6.5 =100×6.5 =650,改：,改：,0.96×201 =0.96×（200+1） =0.96 ×200+0.96 ×1 =192+0.96 =192.96,一、火眼金睛,0.8×0.5×1.25×0.4 =(0.8×1.25)+(0.5×0.4) =1+0.2 =1.2,0.96×201 =0.96×200+1 =192+1 =193,改：,改：,0.8×0.5×1.25×0.4 =(0.8×1.25) ×(0.5×0.4) =1×0.2 =0.2,二、把左右相等的式子用线连起来。,（5+8）×0.4 9×5+9×1.6 4.6×19+5.4×19 5×0.4+8×0.4 9×(5+1.6) (4.6+5.4) ×19 3.6×4×2.5 3.6×(4×2.5),三、能用简便方法的就用简便方法，并说一说运用了哪些运算定律。,0.034×0.5×0.6,4.75×994.75,101×0.45,2.73×99,2.5×3=7.5(元）,5×2=10(元）,10+7.5=17.5(元）,2.5×3+5×2 =7.5+10 17.5（元）,李叔叔买了5箱饮料，一箱有24瓶，每瓶1.3元，共需要多少钱？,1.3×24× 5 =31.2×5 =156（元）,（2）24×5×1.3 =120×1.3 =156（元）,小,理解整数乘法的运算定律对于小数同样适用，并会运用乘法的运算定律进行一些小数的简便计算。,结,