Formula for dividing a cell

Not sure if there is an answer to this question in a previous thread or FAQ, so i appologise if this is so but im short on time and need to see if my problem can be resolved or not.

Not sure if excel can do this or not so here goes,

I have a spreadsheet that i use to enter in daily till information. The entries consist of 24 different group amounts. There is sometimes a discount amount that needs to be taken off specific groups to balance. This has to be done manually before i enter the amounts in, eg: say the discount is £150 i will divide this by 5 and minus that figure from a set amount of groups. Is there anyway i can enter all these amounts then put the discount amount in a new cell at the end that will perform this action for me?

Thanks for any help in advance, i hope i have made myself clear.

i hope i have made myself clear

Not entirely. How do you determine which groups need to have a pro-rated discount subtracted?

Is there anyway i can enter all these amounts then put the discount amount in a new cell at the end that will perform this action for me?

Enter the discount amount in one cell (say A1) and the divisor in another cell (say B1).
In C1 use this formula: =A1/B1

Then simply reference C1 in your "group cell" formula.
Example:
A15 formula: =SUM(A2:A10)-C1

Since your post lacks detail, the above may not be the solution you need. If it isn't, post a sample workbook and provide more clarity about what you need to accomplish. The workbook should contain an example of the desired results.