[Tutor] summing lists

[Hs Hs]

Hi:

I have 4 lists:

>>> a
[40]
>>> b
[2]
>>> c
[23]
>>> d
[12]


how is it possible to do add elements in list. I can do this using tupples, but I do not know how to append elements to tuple, thats the reason I am using list. 

I want to find the value of a+c/a+b+c+d - which is 40+23/40+2+23+12. 

Any help appreciated. 

thanks
Hs.
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