10.2 The following data show the gross trading profits of companies, 1987–1992, in the UK, in £m. 1987 1988 1989 1990 1991 1992 61 750 69 180 73 892 74 405 78 063 77 959

(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?