让我们一步步排查你公式里的问题，然后给出修正后的可用版本：

原公式的核心错误点 #

• 空白单元格判断逻辑错误：你写的R2=" "是判断单元格内容为单个空格，但如果是真正的空白单元格，应该用ISBLANK(R2)或者R2=""
• IF函数语法混乱：多个IF的参数不符合IF(条件, 满足时返回值, 不满足时返回值)的规则，比如IF(R2>54,R2<=64,"F 55 to 64"这里，你把第二个条件错误拆成了参数，正确做法是用AND()把两个条件合并成一个判断
• 括号不匹配：整个公式的嵌套括号数量不对，缺少多个闭合括号，导致Excel无法解析
• 大小写不统一：后面的r2应该统一为R2（虽然Excel不区分大小写，但统一写法更易维护）
• 最后一个IF的结构错误：if((r2>74,"H 75 and over"))多了冗余括号，且参数结构不完整

修正后的完整公式 #

=IF(ISBLANK(R2),"I Unknown",
    IF(AND(R2>0,R2<15),"A Under 15",
        IF(AND(R2>=15,R2<=24),"B 15 to 24",
            IF(AND(R2>24,R2<=34),"C 25 to 34",
                IF(AND(R2>34,R2<=44),"D 35 to 44",
                    IF(AND(R2>44,R2<=54),"E 45 to 54",
                        IF(AND(R2>54,R2<=64),"F 55 to 64",
                            IF(AND(R2>64,R2<=74),"G 65 to 74",
                                IF(R2>74,"H 75 and over","I Unknown")
                            )
                        )
                    )
                )
            )
        )
    )
)

更简洁的替代方案（规避嵌套IF的繁琐） #

如果你的Excel版本支持SWITCH函数（Office 365/2021及以上），可以用更清晰的写法：

=IF(ISBLANK(R2),"I Unknown",
    SWITCH(TRUE,
        AND(R2>0,R2<15),"A Under 15",
        AND(R2>=15,R2<=24),"B 15 to 24",
        AND(R2>24,R2<=34),"C 25 to 34",
        AND(R2>34,R2<=44),"D 35 to 44",
        AND(R2>44,R2<=54),"E 45 to 54",
        AND(R2>54,R2<=64),"F 55 to 64",
        AND(R2>64,R2<=74),"G 65 to 74",
        R2>74,"H 75 and over",
        "I Unknown"
    )
)

或者用LOOKUP函数，利用区间匹配的特性（需确保区间为升序）：

=IF(ISBLANK(R2),"I Unknown",
    LOOKUP(R2,
        {0,15,25,35,45,55,65,75},
        {"A Under 15","B 15 to 24","C 25 to 34","D 35 to 44","E 45 to 54","F 55 to 64","G 65 to 74","H 75 and over"}
    )
)

这个LOOKUP版本的逻辑是：找到小于等于R2的最大区间值，返回对应的分段文本，代码更简洁且易修改。

内容的提问来源于stack exchange，提问作者HelpPlease