Let the total volume of ice-berg is V and its density is ρ. If this ice-berg floats in water with volume Vin  inside it then Vinσg=Vρg⇒Vin=ρσV or Vout =V−Vin=σ−ρσV⇒Vout V=σ−ρσ=1000−9001000=110∴Vout =10% of V