Single-family homes were sold at an annual rate of 3.11 million units nationwide last month, according to a survey by the National Assn. of Realtors. This was up from a June sales pace of 3.06 million units and was the fastest rate since October, 1980. The July survey found that the median sales price of an existing home rose $1,700 to $77,900, 5% above last year. Most of the July increase came from a sharp jump in the West, where the median price rose $6,900 to $100,700. This came even though the West was the only region to show a decline in sales last month, a 9.3% drop that followed a 1.8% decline in June.