某地区居民收入的方差为900,随机抽取400户调查，则调查户平均收入的方差为 ( )。[西安交大2007研]

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30462' and id < 2461243 and id<>'2461243' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30462' and id > 2461243 and id<>'2461243' order by id asc limit 5