Many of the tricky questions from sample papers have been asked and answered here already. To check your question:

1. click on "Search" on the top right of the screen
2. put a few distinctive words from the question in the Search for keywords: field
3. select "MATHS" in the Search in forums: list (you'll have to scroll down a little)
4. select "First post of topics only"
5. click the Search button

For example: searching for "milkman baker".

If you can't find your question, please ask away!