[math4] Activity: adding/subtracting whole numbers

[John Posner]

David Farning wrote:
> FWIW, using git as a version control system is actually pretty easy
> and very useful.  But creating the key and getting stated can be a
> pain.
>   

+1  (from a veteran of the ClearCase and AccuRev commercial 
version-control systems)

Thanks, David!  -John