To form an image twice the size of the object using a convex lens of local length 20 cm, the object distance must be
< 20 cm and between 20 cm and 40 cm
For virtual image, u < f and for real image, u lies between f and 2f, where u is the object distance and f is the focal length. Here, for virtual image, object distance should be less than 20cm and for real image, object distance must be between 20cm and 40cm.