I have a small table which is 12 rows deep.

It can be simplified and summarised as follows;

A B C D
1 10 1 2
2 5 1 3
3 16 2 2
4 1 3 2
5 13 4 3
6 16 4 2
7 17 1 3
8 18 3 3
9 12 5 3
10 12 6 2
11 14 7 2
12 16 2 2

Colum A can contain any value, Colum B is restricted to integers 1-8, and
Colum C is restricted to either 2 or 3.

I require Colum D to show the sum of ("A#"/"C#") for each row which has the
same number in Colum B and then list it against the first row with that
number only

thus the completed table would be as follows

A B C D
1 10 1 2 12.3
2 5 1 3
3 16 2 2 16.0
4 1 3 2 6.5
5 13 4 3 12.3
6 16 4 2
7 17 1 3
8 18 3 3
9 12 5 3 4
10 12 6 2 6
11 14 7 2 7
12 16 2 2

Ive searched and found partial solutions but cant seam to work out a string
to go in the Colum D cells that will do it all.

Thanks in advance.