A convex lens of focal length 20cm and a concave lens of focal length f are mounted coaxially 5cm apart. Parallel beam of light incident on the convex lens emerges from the concave lens as a parallel beam. Then, f in cm is

A convex lens of focal length 1.0m and a concave lens of focal length9.25m are 0.75m apart. A parallel beam of light is incident on the convex lens. The beam emerging after refraction from both lenses is

A convex lens of focal length 1.0m and a concave lens of focal length 0.25m are 0.75m apart. A parallel beam of light is incident on the convex lens. The beam emerging after refraction from both lenses is

A convex lens of focal length 80 cm and a concave lens of focal length 50cm are placed in contact. The resulting will be—

A convex lens of focal length 10cm and concave lens of focal length 20 cm are kept 5 cm apart. The focal length of the equivalent lens is

A convex lens of focal length 100 cm and a concave lens of focal length 10 cm are placed coaxialiy at a separation of 90 cm. If a parallel beam of light is incident on convex lens, then after passing through the two lenses the beam

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are joined together. The power of the combination will be