1. The problem statement, all variables and given/known data An object is placed 50 cm in front of a convex mirror and its image is found to be 20 cm behind the mirror. What is the focal length of the mirror? 2. Relevant equations 1/d0 + 1/di = 1/f 3. The attempt at a solution 1/50 + 1/20 = 1/-f 70/1000 = 1/-f f = 14.28 cm. The book has this answer listed at -33.3 cm. I'm not sure if the book is incorrect or if I did something incorrectly.