The weekly average rate borrowers were quoted on Zillow Mortgage Marketplace for 30-year mortgages increased slightly last week. Last week's rate was 5.07 percent, up slightly from 5.05 percent the week prior, according to the Zillow Mortgage Rate Monitor, compiled by leading real estate Web site Zillow.com®. Meanwhile, rates for 15-year fixed mortgages were unchanged from the week prior at 4.70 percent, and 5-1 adjustable rate mortgages decreased, down to 4.27 percent from 4.30 percent the week prior.