设随机变量<imgwidth="19"height="17"v:shapes="_x0000_i1256"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image266.png">的均值<imgwidth="68"height="21"v:shapes="_x0000_i1257"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image360.png">,方差<imgwidth="75"height="25"v:shapes="_x0000_i1258"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image362.png">,则<imgwidth="60"height="25"v:shapes="_x0000_i1259"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image364.png">()
①
<imgwidth="54"height="25"v:shapes="_x0000_i1260"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image366.png">
②
<imgwidth="54"height="25"v:shapes="_x0000_i1261"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image368.png">
③
<imgwidth="41"height="18"v:shapes="_x0000_i1262"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image370.png">
④
<imgwidth="41"height="18"v:shapes="_x0000_i1263"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image372.png">