How fast was the 30-year fixed mortgage rate decreasing in the first week of May in 2011 (t = 1)? (Round your answer to two decimal places.)
The average 30-year fixed mortgage rate in the United States in the first week of May in 2010 through 2012 is approximated by
M(t)= 55.9 / t^2-0.31t+11.2
percent per year. Here t is measured in years, with t = 0
corresponding to the first week of May in 2010.