The following data show the gross trading profits of companies, 1987–1992, in the UK, in £m. (a)…

The following data show the gross trading profits of
companies, 1987–1992, in the UK, in £m.

(a) Turn the data into an index number series with 1987 as
the reference year.

(b) Transform the series so that 1990 is the reference year.

 (c) What increase has there been in profits between 1987
and 1992? Between 1990 and 1992?