(Q13) For each book whose price is greater than the average price, return the title of the book and the amount by which the book's price exceeds the average price.

<result>
   LET $a := avg(//book/price)
   FOR $b IN /book
   WHERE $b/price > $a
   RETURN
      <expensive_book>
         $b/title ,
         <price_difference>
            $b/price - $a
         </price_difference>
      </expensive_book>
</result>

XSLT equivalent to (Q13)

<result xsl:version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:variable name="avgPrice" select="sum(//book/price) div count(//book/price)"/>
  <xsl:for-each select="/bib/book[price > $avgPrice]">
    <expensive_book>
      <xsl:copy-of select="title"/>
      <price_difference>
        <xsl:value-of select="price - $avgPrice"/>
      </price_difference>
    </expensive_book>
  </xsl:for-each>
</result>