i am on 20th floor, fanling, on average, we get 1 mosquito a year ( presumable, pot luck as it may have caught the lift as they can fly above 15 floors due weak wings)
in sha tau kok, rural house, 3rd floor, taking precautions with screened windows, average 2 a month, probably from lounge window or stairs
without taking precautions, probably 5 per a night!!