Question on data in datagrid /listbox and looping?

Greets All,

Question on data in datagrid /listbox and looping?

I’m trying to decide the best way to write this code.
1 would like the user to make several selections from one listbox/combo box that would
Populate another Listbox/datagrid. Then it would cycle through the selections made in the populated listbox/datagrid and do some calculations. The calculations made would have to add the first two numbers in the populated listbox/datagrid then divide by 25 then divide by 2. Then take that answer and add it to the next populated number in the listbox/datagrid then divide by 25 the divide by 2.

Example: Variable List of Numbers in populated Listbox/combo Box
10,20,30,….

Example of Calculation formula:
1) (((10+20) /25) /2) =.6
2) (((.6+30)/25)/2) =.612
3) Next number in populated listbox/datagrid
Question:
1) Should I use a listbox/datagrid to populate the data with?
2) Is this possible? :-)
3) Any ideas how to write this array loop if possible?

TIA