The third proportional to 0.8 and 0.2 is :

If the third proportional be x,then
0.8 : 0.2 : : 0.2 : x
⇒ 0.8 × x = 0.2 × 0.2

⇒ x =	0.2 × 0.2
	0.8

=	4	= 0.05
	80

Second Method :
Third proportion

=	b²	=	(0.2)²
	a		0.8

=	0.04	= 0.05
	0.8