Suppose I roll an n-sided die once. Now you repeatedly roll the die until you roll a number at least as large as I rolled. What is the expected number of rolls
you have to make?
I know the answer to this problem, but I'm curious about possible solutions people might post.
Answer
If you roll a k, then there are n−k+1 possible numbers out of n that will be greater than or equal to k. This gives rise to a geometric distribution, and so the expected number of rolls required after rolling a k is nn−k+1. Averaging over all k, the expected number of rolls will be E=1nn∑k=1nn−k+1=Hn
where Hn is the nth harmonic series.
No comments:
Post a Comment