Written contracts were up and days on the market for houses were down in the month of August, according to statistics released by the Des Moines Association of Realtors yesterday. Contracts written were up 8 percent compared with July. Homes in the Des Moines metro sold an average of eight days sooner than in July, making August the second-fastest-selling month of the year. The average sales price increased from $167,154 in July to $176,932 in August, up 6 percent.