The average rate on the U.S. 30-year fixed mortgage dropped below 4 percent this week, near historic lows reached a few weeks ago. Low rates are making home-buying and refinancing more affordable. Here\'s a look at rates for fixed- and adjustable-rate mortgages over the past 52 weeks: Current avg.Last week52-week high52-week low30-year fixed3.994.084.913.8715-year fixed3.233.34.133.135-yr adjustable2.92.963.782.801-yr adjustable2.782.843.262.72All values are in percentage points.Source: Freddie Mac Primary Mortgage Market Survey