单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,小数的加法和减法,小数加减混合运算,一、复习旧知,4,82,234,66,4,82,（,234,66,）,248,66,314,482,300,182,你能先说出下面题目的,运算顺序，再计算吗？,有括号时，就先,算括号里面的。,整数加、减混合运算，一般从左往右算。,4,.,6,9,二、探究新知,（,1,）小刚买了下面,3,本书，一共花了多少钱？,7,.,45,5,.,8,4,.,69,9,4,1,7,5,.,8,1,.,7,.,4,5,17,.,94,（元）,1,7,.,45,5,.,8,4,.,69,13,.,2,5,4,.,69,答：一共花了,17,.,9,4,元,。,17,.,94,（元）,我这样算。,我这样算。,二、探究新知,（,2,）小林付给售货员,20,元，应找回多少钱？,20,6,.,45,8,.,3,13,.,55,8,.,3,5,.,25,（元）,20,（,6,.,45,8,.,3,）,20,14,.,75,5,.,25,（元）,答：应找回,5,.,25,元。,我这样算。,我这样算。,小林,二、探究新知,（,2,）小林付给售货员,20,元，应找回多少钱？,20,6,.,45,8,.,3,13,.,55,8,.,3,5,.,25,（元）,20,（,6,.,45,8,.,3,）,20,14,.,75,5,.,25,（元）,小林,算式,20,（,6,.,45,8,.,3,）,与算式,20,6,.,45,8,.,3,是,相等的。,观察这两个综合算式,你有什么发现？,二、探究新知,7,.,45,5,.,8,4,.,69,13,.,2,5,4,.,69,17,.,94,（元）,20,6,.,45,8,.,3,13,.,55,8,.,3,5,.,25,（元）,20,（,6,.,45,8,.,3,）,20,14,.,75,5,.,25,（元）,如果有括号，要,先算,括号里面,的。,和整数加、减混合运算的方法一样,按照从左往右的,顺序计算。,小数加、减法混合运,算，该怎样计算呢？,三、知识运用,0,.,38,0,.,26,2,.,6,5,.,7,0,.,81,1,.,29,9,8,.,2,32,.,5,13,.,4,0,.,64,2,.,6,3,.,24,4,.,89,1,.,29,3,.,6,130,.,7,13,.,4,117,.,3,1.,请脱式计算下面各题。,三、知识运用,2.,你会用计算器计算小数,加、减混合运算吗？,你是怎样输入的，请把它,记录下来，并计算出结果。,三、知识运用,2.,从左往右算，先,算,50,38,.,5,，再,算减,4,.,8,。,你知道计算器是按什么,运算顺序计算的吗？,50,38,.,5,4,.,8,6,.,7,50,（,38,.,5,4,.,8,）,6,.,7,我先算括号里的,38,.,5,4,.,8,，把答,案记下来，再用,50,减去它。,三、知识运用,1,.,1,0,.,15,0,.,09,1,.,25,0,.,09,1,.,16,（,m,）,答：肖红跳过了,1,.,16,m,。,肖红跳过了多少米？,你还能提出什么,数学问题并解答？,3.,四、布置作业,作业：,第,77,页练习十八，第,4,题；,第,78,页练习十八，第,7,题,、第,8,题。,