let $auction := doc("http://monetdb.cwi.nl/xmark/auctions.xml") return
<result>
  <preferred>
    {count($auction/site/people/person/profile[@income >= 100000])}
  </preferred>
  <standard>
    {
      count(
        $auction/site/people/person/
         profile[@income < 100000 and @income >= 30000]
      )
    }
  </standard>
  <challenge>
    {count($auction/site/people/person/profile[@income < 30000])}
  </challenge>
  <na>
    {
      count(
        for $p in $auction/site/people/person
        where empty($p/profile/@income)
        return $p
      )
    }
  </na>
</result>