Sales of existing single-family homes in Maine increased 15 percent in August over a year ago, with the median sales price rising 3 percent. The Maine Association of Realtors says real estate agents last month sold 1,255 homes in Maine, up from 1,090 in August 2011. The median sales price was $170,000, up from $165,000 a year earlier. For the three-month period from June through August, the number of home sales rose in 14 of Maine’s 16 counties. The highest-priced homes were in Cumberland County, where the median sales price was $229,900. The lowest-priced homes were in Aroostook County, where the median sales price was $80,000.