Index numbers are a useful way of expressing pieces of information and collections of data. This tutor2u article shows you how to express data in index number format and some examples of data which is commonly presented as an index number.
http://tutor2u.net/economics/revision-notes/as-macro-using-index-numbers.html
Bized worksheet on index numbers: http://www.bized.co.uk/learn/economics/macro/indnos/student.htm
Bized answers to worksheet: http://www.bized.co.uk/learn/economics/macro/indnos/tutor.htm
