Figure shows a point object placed in front of a transparent sphere of radius 20 cm and refractive index 1.5. The sphere forms an image due to refraction at surface I followed by refraction at surface II. The sphere is kept in air and the object is located at distance x from P_(1). It is found that for x gt x_(1), the image formed due to refraction at surface I is real, the final image formed by the sphere is also real and forms to the right of P_(2). For x_(2) lt x lt x_(1), the image formed by surface I is virtual while the final image formed by the sphere is real and forms to the right of P_(2). However for x lt x_(2), the image formed by surface I and also the final image formed by the sphere are virtual. It is also found that the final image is virtual if the distance of image formed by surface I from P_(2) is less than y. The object is now moved away from the sphere so that x becomes large and say, x to oo. In the given sphere is replaced by another one of the same radius but of refractive index 2.5, the final image is formed at distance y_(2) from P_(2). As stated above, if the distance of image formed by Surface 1 from P_(2) is less than y, the final image is virtual. Then, y will be