best resource for GCSE maths? (books/online)

[vannah]

I work in primary maths so havent really a clue about secondary maths.What would you say is the best revision book or website for intensive revision? A friend has asked me...

and how can they do online numeracy tests?
thanks

I retook my math GCSE last year and I found the most useful website was bbc bitesize.

CGP Fuides are generally very good for GCSE.

or guides!