A small statue has a height of 3.8 cm and is placed in front of a concave mirror. The image of the statue is inverted, 1.9 cm tall, and located 14 cm away from the mirror. Find the focal length of the mirror.

Answer 1

The image is real (because it is inverted)and the magnification is 1.9/3.8 = 1/2.
The image distance di is half the object distance do. (do = 2 di)
1/di + 1/do = 3/do = 1/f
f = do/3 = 2 di/3 = 9.33 cm

Check:
1/28 + 1/14 = 1/9.33