August home and condo sales in Massachusetts increased 15% over last year, making it the first time both types of housing experienced a sales increase in the same month, The Warren Group said in a report this week. During August, 4,203 single-family homes sold in the Bay State, a 15% jump from 3,652 sales in August of last year. “On the surface, the August numbers appear to be very strong. But we’re comparing sales volume to a month last year when buyers were retreating after the tax credits expired,” said Cory Hopkins, managing editor of Banker & Tradesman, publisher of The Warren Group report. The median price of single-family homes in Massachusetts slid 3.4% to $305,700 in August, compared to $316,500 last year. However, that is up from the first part of the year when the median hovered around $296,000. Condo sales alone increased 5.8% in August from a year ago, with 1,716 units sold compared to 1,622 from last year. Write to Kerri Panchuk.