A convex lens of focal length 20cm is placed coaxially with a concave mirror of focal length 10cm at a distance of 50cm apart from each other. A beam of light coming parallel to the principal axis is incident on the convex lens. Find the position of the final image formed by this combination.

Since rays are coming from infinity
For first image
1/u + 1/v = 1/f
f = 20cm
u > 2f therefore infinity
1/v = 1/20
v = 20cm
for second mirror is placed it can be
1/u + 1/v = 1/f
u = 30cm = infinity since greater than 2f
f = 12cm
therefore 1/v = 1/12 + 1/30
v = 17cmagain applying the lens formula for the lenses
1/v - 1/u = 1/f
u = 30cm
f = 20cm
v = 46.6cm to the left of the lens.