%%
%% Time (in minutes) to run a marathon depends 
%% on 3 variables:
%%
%%  x1 = ponderal index = 
%%     = height(ins)/(weight(lbs))^(1/3)
%%  x2 = miles run previous 8 weeks
%%  x3 = age 
%%
%% Find model by linear regression. 
%% Time ~= a1 * x1 + a2 * x2 + a3 * x3 + var
%% Estimate your time to run a marathon
%% 
%% Data:  5 samples given 
%%
%% 
disp('    tim        x1        x2        x3');
%%   Time   x1     x2   x3: 
A = [ 181   13.1  619   23;
      193   13.5  803   42;
      212   13.8  207   31;
      221   13.1  409   38;
      248   12.5  482   45 ]
