p_n = 0.6*p_n-1+0.4*(1-p_n-1) 

       = 0.2*p_n-1+0.4

p_n -0.5 = 0.2*(p_n-1 - 0.5) 

p_n = 0.5+0.2^(n-1)*(p1-0.5)

p1 = 1/2 *0.6 + 1/2 *0.4 = 0.5;

p_100 = 0.5.