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Just in time for the busiest home shopping season of the year, mortgage rates continue to fall, this week dipping below 4 percent for the first time since November, according to Freddie Mac's Primary Mortgage Market Survey.

The results of that weekly survey for the week ending April 20:

• The 30-year fixed-rate mortgage (FRM) averaged 3.97 percent with an average 0.5 point, down from last week when it averaged 4.08 percent. A year ago at this time, the 30-year FRM averaged 3.59 percent.

• 15-year FRM this week averaged 3.23 percent with an average 0.5 point, down from last week when it averaged 3.34 percent. A year ago at this time, the 15-year FRM averaged 2.85 percent.

• 5-year Treasury-indexed hybrid adjustable-rate mortgage (ARM) averaged 3.10 percent this week with an average 0.4 point, down from last week when it averaged 3.18 percent. A year ago, the 5-year ARM averaged 2.81 percent.

Freddie Mac's chief economist, Sean Becketti, said that weak economic data and growing international tensions are driving investors out of riskier sectors and into Treasury securities. "This shift in investment sentiment has propelled rates lower," he said.