Someone is looking for a cat in one of thirty trees. The probability of the cat being an any tree is the same for all trees.
What is the expected value and variance of the number of trees that need to be searched to find the cat?
The probability of finding the cat in precisely the kth tree and not an earlier tree is always
The mean is easy:
To calculate variance, we first find:
So, the variance is:
That variance seems too high to be right. Is it wrong? How so?