collating information

If you have a spreadsheet where column A is a list of names, for each name there are several data types (listed in column B) some of the data types are repeated. Column C contains the percentage for each of the data tpes for the whole thing. There are 300+ names, each with several data types and most where at least one data type is repeated. How can i easily calculate the total percentage for each data type, for each name.

eg.

Column A            Column B           Column C
Site A              Grassland          12.00
Site A              Inland Water       7.00
Site A              Mixed Woodland     30.00
Site A              Grassland          33.00
Site A              Grassland          18.00

At present I have been creating a sum function for each data type and then deleting the rows that I don't need to neaten it up. But this is very time consuming and like I said I have to do this over 300 times.

Any help on this would be great,
Cheers
B2B