分数和小数的互化 (4)

状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,五年级下册,船山区裕丰街小学 教师：陈迎春,第,2,课时 分数和小数的互化（,2,）,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,把小数化成分数时,原来有几位小数,就在,1,的后面写几个,0,作分母,原来的小数去掉小数点作分子,。不是最简分数的要化成最简分数。,小数化成分数的方法：,如果要把分数化成小数，该怎么做呢？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,2,把 化成小数（除不尽的保留两位小数）。,探究新知,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,10,7,0,.,7,100,39,0,.,39,（,1,）、写成小数分别是多少？,分母是,10,，,100,，,1000,，,的分数化成小数，,可以直接去掉分母,，,看,1,后面有几个,0,，就在分子中最后一位起向左数几位，点上小数点。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,（,2,）、写成小数分别是多少？,利用分数与除法的关系，用分子除以分母,得出小数。,4,3,340,.,75,40,9,9400,.,225,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,9,2,29,0,.,22,14,5,514,0,.,36,分母不是,10,，,100,，,1000,，,的分数化成小数，,用分子除以分母,，,如果分子除以分母除不尽，要根据需要按“四舍五入”法保留几位小数,。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,把,0.7,、,0.25,、,这,6,10,9,100,43,25,7,47,13,个数按从小到大的顺序排列起来。,做一做,这,6,个数中，有分数、有小数，要比较这些数的大小，该怎么办？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,10,9,0,.,9,100,43,0,.,43,25,7,7250,.,28,13470,.,277,47,13,0,.,25,47,13,25,7,100,43,0,.,7,10,9,若是把小数转化成分数怎么做呢？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,达标检测,1.,填空,把 化成小数时，整数部分不变，直接去掉分母，看分母,1,后面有几个,0,，就在分子中从（）起，向（）数出（）位，点上（）结果是（）。,最后一位,左,3,小数点,1.007,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,2.把下面的分数化成小数（,不能化成有限小数,的保留两位小数）。,100,31,25,2,30,7,9,4,6,5,50,11,20,23,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,100,31,25,2,30,7,9,4,6,5,50,11,20,23,100,31,=,0.31,25,2,=,225=0.08,30,7,=,7300.23,=,49 0.44,9,4,6,5,=,56 0.83,50,11,=,1150=0.22,20,23,=,2320=1.15,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,3.,下面的分数与小数的互化是否正确？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,4.,把下面的小数和与它相等的分数用线连起来。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,方法一：,0.9 60=54,（个）,54,50,李阿姨和王叔叔谁打字快些？,方法二：,=560.83,（个）,0.9,0.83,6,5,我平均每秒打,0.9,个字。,我,1,分钟打了,50,个字，平均每秒打了,个字。,5.,1.,分母是,10,，,100,，,1000,，,的分数化成小数，,可以直接去掉分母,，,看,1,后面有几个,0,，就在分子中最后一位起向左数几位，点上小数点。,分数化成小数的方法：,2.,分母不是,10,，,100,，,1000,，,的分数化成小数，,用分子除以分母,，,如果分子除以分母除不尽，要根据需要按“四舍五入”法保留几位小数,。,课堂小结,1.,怎样判断什么样的最简分数可以化成有限小数？,2.,你能举例来说说吗？,3.,为什么可以这样判断？,拓展提升,下面这些分数中哪些可以化成有限小数？,判断前看分数是不是最简分数,把最简分数的分母分解质因数：,8=222,40=2225,21=37,30=235,现在你知道哪些分数可以化成有限小数了吗？,1.,课本练习十九，第,5,、,6,、,8,题；,2.,完成练习册本课时的习题。,课后作业,