Rates on 30-year mortgages stayed below 5 percent again this week. The average rate for a 30-year fixed mortgage fell to 4.83 percent, down from 4.91 percent. Last year at this time, 30-year mortgages averaged 6.04 percent. This week the average rate on a 15-year fixed-rate mortgage fell to 4.32 percent and rates on five-year, adjustable-rate mortgages averaged 4.25 percent. According to Freddie Mac, the best rates usually are available only to borrowers with solid credit and a 20 percent down payment.