A useful link for A Level Economics relating to variable costs http://www.bbc.co.uk/news/uk-politics-44229606 and where to find the relevant section within the spec:
Edexcel spec reference 3.3.2 a) Formulae to calculate
- o average variable cost
AQA spec reference 22.214.171.124 The difference between fixed and variable costs.
OCR spec reference P10 Explain what is meant by: average variable cost (AVC)