Magnification by Thin Lenses

Q. In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm, where should an object be placed

1. 50 cm
2. 30 cm
3. – 50 cm
4. – 30 cm

Q. The objective lens of a compound microscope produces magnification of $10$. In order to get an overall magnification of $100$ when image is formed at $25cm$ from the eye, the focal length of the eye piece should be

1. $4cm$
2. $10cm$
3. $\frac{25}{9}cm$
4. $9cm$