Long-term mortgage rates dipped in the latest week, according to Freddie Mac, marking four consecutive weeks of declines. The average rate on a 30-year fixed-rate mortgage (FRM) slipped to 4.06% with an average 0.5 point for the week ended May 23, down from 4.07% the week before and from 4.66% a year earlier. Rates on 15-year FRMs also fell, decreasing to an average of 3.51% with an average 0.4 point, down from 3.53% the previous week and 4.15% a year ago.