Xavier J. answered 06/11/13
Tutor in Math, topics range from Algebra to Calculus.
Are you asking how to calculate the % of how many users are performing exactly one activity? If so then you find out what % among all users are performing whichever activity you would like to start with then subtract that from the percent of those performing both tasks.
This type of question is very common in classes that introduce basic set theory.
We can let "A" represent the number of people performing activity 1 and "B" represent the number people performing activity 2 and "A and B" represent the number of people performing activity 1 and 2.
P(A) would then represent the % of people performing activity 1 and likewise for P(B) and P(A and B).
Using these symbols, an algebraic way to express the answer would be to say P(A and not B) = P(A) - P(A and B).
I hope this helps.