Find the third proportional between 9 and 27.

Let the third proportional be x . Since the third proportional to 9 and 27 is the same as fourth proportional to 9,27,27
∴ 9 : 27 : : 27 : x

∴	9	=	27
	27		x

⇒ 9 × x = 27 × 27

⇒ x =	27 × 27	= 81
	9