It's the classic "lying philosophers" puzzle.
No that is not it. The person who put the krugerrand under the ashtrays knows which one its under and therfore whether or not its under my first choice. However he is not trying to psych me. Irrespective of whether or not the coin is under my choice he was always going to ask me if I wanted to change.
Although there are now only 2 ashtrays my friend says my odds of getting the valuable coin are much better than 50:50 if I swap from my original choice and chose the other one.
What is my best chance of getting the coin;
a) Stick with my original choice.
b) Change my choice and choose the other ashtray.
c) It does not make any difference which I choose.