MIDDLE-INCOME families will have the chance to buy more low-priced flats in September. For sale will be 800 units in a project in Ma On Shan, scheduled for completion by the end of next year for the so-called sandwich classes, according to Housing Society plans. The society said it might extend its preferential mortgage terms. It is offering 80 per cent mortgages to buyers of its first 1,024 sandwich-class flats on Tsing Yi Island, which are sold at two-thirds of market value. The society's executive director Victor So Hing-woh said: 'The pre-sale of the Ma On Shan units will be held around September. It is too early to talk about pricing or mortgage terms.' He said the society would negotiate with banks at a later stage of the planned sale. Mr So, with executive committee member Sir David Akers-Jones, yesterday officiated at a computer balloting to decide the order of interviews with the 4,373 applicants for the Tsing Yi Island units. Families will be asked to attend interviews after the Lunar New Year holidays and interviews will end when all 1,024 flats are sold. Results of the balloting will be published in the South China Morning Post tomorrow.