Where should an object be placed so that a real and inverted image of the same size is obtained by a convex lens?

$A$ student focused the image of a candle flame on a white screen by placing the flame at various distances from a convex lens. He noted his observations:

Observation	Distance of flame from the lens $(cm)$	Distance of screen from the lens $(cm)$
$(i)$	$60$	$20$
$(ii)$	$40$	$24$
$(iii)$	$30$	$30$
$(iv)$	$24$	$40$
$(v)$	$15$	$70$

$(a)$ From the above table, find the focal length of the lens without using the lens formula.
$(b)$ Which set of observations is incorrect and why?
$(c)$ In which case will the size of the object and the image be the same? Give a reason for your answer.

When an object is placed at $2F$ in front of a convex lens,where will its image be formed?

State the relation between object distance,image distance,and focal length of a concave or convex mirror. $A$ concave mirror produces a two times magnified real image of an object placed at $10 \ cm$ from it. Find the position of the image.

$A$ virtual,magnified and erect image can be formed by a concave mirror.

Name the type of lens that can be used to obtain:
$(i)$ $A$ magnified and virtual image.
$(ii)$ $A$ diminished and virtual image of the object.