Central Board Of Secondary Education [CBSE] — board class 10 science question paper

Pls look at the question based on light chapter question no 18 code no-31/3/3 that states that the focal length of a convex lens is 20cm and the image of the object is diminished to 1/3rd the size of object. Find the object distance. After proper calculation the answer is -40 cm and it's impossible since the object will be placed "at 2f¹ and thus the object will also formed"at 2f²". If that's the case the object will be of same size but the question stated that it's diminished. Hence its wrong. Pls view my concern thoroughly. Also another question no 3 based on presbyopia was given where the diagram was asked which is no where in ncert text. Hence marks should be given.