问题
填空题
数据3、1、x、-1、-3的平均数是0，则这组数据的方差是______．
答案
由题意可知
因为平均数为0
则
（3+1+x-1-3）=01 5
求得x=0，
所以方差S2=
[（3-0）2+（1-0）2+（0-0）2+（-1-0）2+（-3-0）2]=41 5
故填4．
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数据3、1、x、-1、-3的平均数是0，则这组数据的方差是______．
由题意可知
因为平均数为0
则
（3+1+x-1-3）=01 5
求得x=0，
所以方差S2=
[（3-0）2+（1-0）2+（0-0）2+（-1-0）2+（-3-0）2]=41 5
故填4．
Homesick is a compound (复合的) word made up of HOME and SICK. You know what each means on its own, of course. But do you know the meaning they are used together? The definition (定义) of homesick is SICK FOR HOME. It means you miss your home. Now think for a minute SEASICK. If you change the word HOME in the definition to the word SEA, would the definition SEASICK? Does seasick mean SICK FOR SEA? It means something quite . Seasick means SICK BY THE MOVEMENT ON THE SEA. When you are , the only place you want to be is at home. When you are seasick, you want to be is at sea. Have you ever a person being heartsick? Heartsick doesn’t mean that something is wrong with a person’s heart. People are heartsick when they are deep inside as if (好像) their hearts are broken. And we also have other compound words, such as handshake and . Perhaps you may write definitions for them. It must be helpful to know something like this in your English study.
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