gistfile1.rb

require 'nokogiri'

doc = Nokogiri::XML(<<-eoxml)
<stores>
  <store name="store a">
    <book>awesome</book>
    <book>examples</book>
    <book>are</book>
    <book>awesome</book>
  </store>
  <store name="store b">
    <book>awesome</book>
    <book>examples</book>
  </store>
</stores>
eoxml

doc.xpath('//store[count(book) > 2]').each do |store|
  puts store['name']
end