The third propotional to 0.8 and 0.2 is ?

Let 0.8 : 0.2 : : 0.2 : N
Then 0.8 x N = 0.2 x 0.2
∴ N = ( 0.2 x 0.2) / 0.8 = 0.04 / 0.08 = 4/80 = 0.05