A recent Performance exam contained 5 graph related questions which, in total, made up nearly 25% of the marks.
They were based on 4 individual graphs and one had two questions related to it.
It's important that you download and familiarise yourself with the CAP from the CAA website and know how to use them for related questions.
http://publicapps.caa.co.uk/docs/33/CAP698.pdf
The actual graphs used in the exam are provided in a Workbook given in the exam room.
Hope that helps
ArronG