求一个小数的近似数 (2)

1、,求一个小数的近似数,执教者：利川市第一民族实验小学 孙金荣,R四年级下册,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,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,复习导入,1.把下面各数省略“万”位后面的数，求出它们的近似数。,8

2、765346874244200 8604769701021870,2.下面的 可以填上哪些数字？,32 64532万,46 70547万,0、1、2、3、4,5、6、7、8、9,小结：整数中求一个数的近似数，我们用的是“四舍五入”法。,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,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

3、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,探究新知,请同学们说一说豆豆的准确身高是多少？,思考讨论：,1.求小数的近似数可以用什么方法？,2.把0.984保留两位小数是多少？,3.把0.984保留一位小数是多少？,4.把0.984保留整数是多少？,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,状元成才路,状

4、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,0.984保留两位小数：,求小数的近似数的方法：,“四舍五入”法,0.9840.98,保留两位小数，表示精确到百分位，也就是要观察小数部分的第3位。,小于5，舍去。,0.984保留一位小数：,0.9841.0,大于5，向前一位进1，9进1等于10，满10要向前一位进1。,保留一位小数，表示精确到十分位，也就是要观察小数部分的第2位。,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

5、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,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,0.984保留整数：,0.9841,保留整数，表示精确到个位，也就是要观察小数部分的第1位。,大于5，向前一位进1。,0.9841,0.9841.0,0.9840.98,（保留两位小数）,（保留一位小数）,（保留整数）,观察这两个算式，你发现了什么？,我

6、发现1=1.0，但是小数点后面的0不能去掉，因为题目要求保留一位小数，而0起占位的作用。,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,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,归纳总结：,求一个小数的近似数，可以用（ ）的方法；,

7、保留整数时，要观察（ ）； 再四舍五入；,保留一位小数时，要观察（ ）；再四舍五入；,保留两位小数时，要观察（ ）；再四舍五入；,四舍五入,小数部分第一位,小数部分第二位,小数部分第三位,闯关练习,求下面小数的近似数。,（1）0.256 12.006 1.0987 （保留两位小数）,（2）3.72 0.58 9.0548 （保留一位小数）,（1）0.26 12.01 1.10,（2）3.7 0.6 9.1,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

8、,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,闯关练习,1.判一判。,（1）3.98精确到十分位是4,（2）6.05和6.0599保留一位小数都是6.1,（3）0.596保留两位小数是0.6,（4）5.29在自然数5和6之间， 它保留整数约等于6,（ ）,（ ）,（ ）,（ ）,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

9、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,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.填空。,（1）7.996保留两位小数约是（ ）。 （2）6.386精确到百分位约是（ ）。 （3）9.433精确到百分位约是（ ）。 （4）8.995精确到十分位约是（ ）， 精确到百分位约是（ ）。,8.00,6.39,9.43,9.0,

10、9.00,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,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,闯关练习,1.按要求完成表格。,5,19,5,4.5,19.2,4.8,4.52,19.16,4.76,2.猜一猜,张老师称体重的时候，得到一个一位小数，精确到个位约是49千克，张老师的体重最轻是（ ）千克。,48.5,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,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