求一个小数的近似数.ppt

R四年级下册,5.小数的近似数,第1课时四舍五入法求小数的近似数,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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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。,87653468742442008604769701021870,2.下面的可以填上哪些数字？,3264532万,4670547万,0、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,状元成才路,状元成才路,状元成才路,状元成才路,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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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是一个占位符。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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；,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）0.25612.0061.0987（保留两位小数）,（2）3.720.589.0548（保留一位小数）,（1）0.2612.011.10,（2）3.70.69.1,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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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（）。,8.00,6.39,9.43,9.0,9.00,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。,5,19,5,4.5,19.1,4.8,4.52,19.16,4.76,2.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,状元成才路,状