# variance problem

• Oct 10th 2010, 06:23 PM
CarmineCortez
variance problem
Q:
n people put their watch in the center of a room where the watches are mixed
together. Each person then randomly selects one. Let X represent the number that select their own watch. Find the expected value and variance of X.

I found the expedted value to be 1. ( sum to n 1/n*1). So variance i have
sum 1/n(x_i - 1)^2 = 0

is the variance correctly 0?
• Oct 10th 2010, 08:44 PM
matheagle
it can't be zero.
that means X is constant, wp1
• Oct 10th 2010, 08:46 PM
mr fantastic
Quote:

Originally Posted by CarmineCortez
Q:
n people put their watch in the center of a room where the watches are mixed
together. Each person then randomly selects one. Let X represent the number that select their own watch. Find the expected value and variance of X.

I found the expedted value to be 1. ( sum to n 1/n*1). So variance i have
sum 1/n(x_i - 1)^2 = 0

is the variance correctly 0?

What you need can be found here: Rencontres numbers - Wikipedia, the free encyclopedia