四年级奥数：最值问题解法举例 标签：速算与巧算
<p>在一定范围内求最大值或最小值的问题，我们称之为“最大最小问题”。“最大”、“最小”是同学们所熟悉的两个概念，多年来各级数学竞赛中屡次出现求最值问题，但一些学生感到束手无策。<b> </b></p><p><b>一、枚举法</b></p><p><b></b><b><font face=" ,Times New Roman">1 </font></b><font face=" ,Times New Roman">4</font><font face=" ,Times New Roman">4</font></p><p><b></b><b><font face=" ,Times New Roman"> </font></b><font face=" ,Times New Roman">3</font><font face=" ,Times New Roman">4</font><font face=" ,Times New Roman">3</font><font face=" ,Times New Roman">2</font><font face=" ,Times New Roman">1</font><font face=" ,Times New Roman">3</font><font face=" ,Times New Roman">2</font><font face=" ,Times New Roman">1=6</font></p><p><b></b><b><font face=" ,Times New Roman">2 </font></b><font face=" ,Times New Roman">x</font><font size="1">3</font><font face=" ,Times New Roman">=84A</font><font face=" ,Times New Roman">x</font><font face=" ,Times New Roman">A</font><font face=" ,Times New Roman">A</font><font face=" ,Times New Roman">______</font><font face=" ,Times New Roman">2023</font></p><p><b></b><b><font face=" ,Times New Roman"> </font></b><font face=" ,Times New Roman">84A</font><font face=" ,Times New Roman">84</font><font face=" ,Times New Roman">84=2</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">2</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">3</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">7</font><font face=" ,Times New Roman">x</font><font size="2">3</font><font face=" ,Times New Roman">=2</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">2</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">3</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">7</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">A</font><font face=" ,Times New Roman">A</font><font face=" ,Times New Roman">2</font><font face=" ,Times New Roman">3</font><font face=" ,Times New Roman">7</font></p><p><font face=" ,Times New Roman">A</font><font face=" ,Times New Roman">2</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">3</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">3</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">7</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">7=</font><font face=" ,Times New Roman">882</font></p><p><b></b><b><font face=" ,Times New Roman">3 </font></b><font face=" ,Times New Roman">43</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font></p><p><b></b><b><font face=" ,Times New Roman"> </font></b><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font></p><p><font face=" ,Times New Roman">43a</font><font face=" ,Times New Roman">b=</font></p><p><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">43b</font><font face=" ,Times New Roman">42</font></p><p><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">23</font><font face=" ,Times New Roman">24</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">43</font><font face=" ,Times New Roman">2023</font></p><p><font face=" ,Times New Roman">a=23</font><font face=" ,Times New Roman">43</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">23</font><font face=" ,Times New Roman">10=999</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">10</font></p><p><font face=" ,Times New Roman">a=22</font><font face=" ,Times New Roman">43</font><font face="宋体" lang="ZH-CN">×</font><font face=" ,Times New Roman">22</font><font face=" ,Times New Roman">42=988</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">42</font></p><p><font face=" ,Times New Roman">a=22</font><font face=" ,Times New Roman">b=42</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">22+42=64</font></p><p><b></b><b><font face=" ,Times New Roman">4 </font></b><font face=" ,Times New Roman">18</font></p><p><b></b><b><font face=" ,Times New Roman"> </font></b><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font><font face=" ,Times New Roman">a</font><font face=" ,Times New Roman">b</font></p><p><font face=" ,Times New Roman">81</font></p><p><b></b><b><font face=" ,Times New Roman">5 </font></b><font face=" ,Times New Roman">9</font></p><p><font face="宋体" lang="ZH-CN"></font></p><p><font face=" ,Times New Roman">10</font><font face=" ,Times New Roman">9</font><font face=" ,Times New Roman">8</font><font face=" ,Times New Roman">7</font><font face=" ,Times New Roman">6</font><font face=" ,Times New Roman">-</font><font face=" ,Times New Roman">1</font><font face=" ,Times New Roman">2</font><font face=" ,Times New Roman">3</font><font face=" ,Times New Roman">4</font><font face=" ,Times New Roman">=30</font></p><p><font face=" ,Times New Roman">30</font></p>
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