A convex lens produces a double size real image when an object is place at a distance of 18 cm from it. Where should the object be place to produce a triple size real image?

the distance between object and the lens, u = 18cm

The magnification of the real image is given as m= -2

Now, using lens maker’s formula,

Now, the required magnification m=-3 =v/u


Hence, the object should be placed 16 cm from lens