求某个数的近似数有哪些方法？

1四舍五入，这最常用
2进一法，
3去尾法
后两种只用在特殊情况
你说的1.保留有效数字；2.精确到某一 这都不是方法，而是取精确数时的要求。

1四舍五入
2进一法
3去尾法
四舍五入是最常用的，后两种只用在特殊情况

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