A convex lens and a concave lens, each having same focal

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is

From the formula,

	1	=	1	+	1	=	1	-	1	= 0
	f		f₁		f₂		25		25

Power of combination =	1	= 0
	f