Using a list to change the value of a cell

[Rodrigues]

Microsoft Office Excel 2007

Here's the thing
I want to change the value inside a cell based on the person's choice of a value in a list.
How do I do that?
For example

Options of List:
A
B
C

If you choose option A, in cell X a certain number will appear, let's say 10
If you choose option B, in cell X another number will appear, let's say 15
And so on

Did I made myself clear? English is not my mother tongue.

Thanks for the help guys.

[turnand]

You can change the formula accordingly.Say the drop down is A1 what you'd want at the moment is
=IF(A1="A","10,IF(A1="B",15,IF(A1="C",20))))