You can do it like this. Put 10 in a cell and copy it.
Select the cell with 100 in it and right click - paste special - select
'ADD' - OK
Delete the 10 from the cell
When competing hypotheses are otherwise equal, adopt the hypothesis that
introduces the fewest assumptions while still sufficiently answering the
> I have a value in a cell eg 100 and want to add another value to it eg 10.
> Can this be done by entering the additional value and the sum completed