How many {operating system} are for {Skype} ?
What is the number of operating systems for Skype?
How many operating systems does Skype have?
SELECT ( COUNT ( ?g ) AS ?w ) { resource:Skype property:operating_system ?g }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q40984> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P306> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q40984 wdt:P306 ?obj }
9