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.