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The Dutchman says the pair interchange between the more forward position, traditionally the number nine spot, and the creative number 10 position linking with midfield. Van Persie has scored 10 goals for United since his summer move from Arsenal - helped significantly by his forming an immediate understanding with Rooney.
Van Persie told the club's official website: "I call it a nine and a half because you have two positions, the nine and the 10, and we are both nine and a half. We are just helping each other out. We both play behind and a bit higher up. It seems to be working well and I am very happy with Wayne - hopefully we can keep it going."
United boss Sir Alex Ferguson said the flexibility to the partnership was key but that the pair had yet to hit the highest level together, even if there were flashes in the 2-1 win over the Gunners at the weekend.
Ferguson said: "There's flexibility there and the right type of movement.
"They also both have the courage to play in these positions. Robin's not far away in that respect.
"They're both mobile players and good footballers with a great desire to play and win.
"I don't think you saw the best of them as a partnership against Arsenal."
Source: PA
Source: PA