Tell me more ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Let $A=\{i: 1 \leq i \leq n\} \subset \mathbb{N} $ and $B \subset A$, $|B|=k$ ($k < n$). What's the probability that $\gcd(B)>1$?

EDIT: $n$ and $k$ are given. I think this can be solved with inclusion-exclusion principle?

share|improve this question
Perhaps it may be useful to know that the probability that a number $k < n$ selected being coprime to $n$ is $\phi(n)/n$. – BenjaLim Aug 5 '12 at 8:42

Know someone who can answer? Share a link to this question via email, Google+, Twitter, or Facebook.

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.