Focal Length of Lens: Object 5 cm Tall, 10 cm Away

[dev-hud]

An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal length of the lens?

I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to start or what equation(s) to use?? :(

 

[berkeman]

An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal length of the lens?

I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to start or what equation(s) to use?? :(

Use the lens equation. Can you show us what that is? And make a sketch. Could you show us a sketch of the situation?