add without carry

[Jon Ribbens]

In article <450a7dec$0$14661$626a54ce at news.free.fr>, Bruno Desthuilliers wrote:
> Hugh wrote:
>> Sorry, here's an example...
>> 
>> 5+7=12
>> 
>> added without carrying, 5+7=2
>> 
>> i.e the result is always less than 10
> 
>> I've been thinking some more about this and my brain is starting to
>> work something out... 
> 
> No need to think too long to come up with the most possibly Q&D solution:
> 
> res = int(str(5 + 7)[-1])

Am I missing something subtle in the question or is there some reason
that nobody has posted the correct solution:

  (a + b) % 10

?