Physics: Converging and Diverging Lenses

[casiocasio442]

Summary:: I cannot seem to get the answer to the following question.
For (a) I am using the formula 1/V= 1/U- 1/F, giving me 7.5cm. I am then adding this to 50cm to get 57.5cm. I then used -1/20-1/57.5-1/v to get **-14.9cm** which is Incorrect.
Any help greatly appreciated!

 

[Dr_Nate]

You could try drawing the ray diagrams to give you an idea of what the answer should be. That might help you think about what you need to do to actually calculate it.

 

[Merlin3189]

Have you tried 14.8?