PREFIX  dc:  <http://purl.org/dc/elements/1.1/>
PREFIX  ns:  <http://example.org/ns#>

SELECT  ?title ?price
{  ?x ns:price ?p .
   ?x ns:discount ?discount
   BIND (?p*(1-?discount) AS ?price)
   FILTER(?price < 20)
   ?x dc:title ?title . 
}
