Suppose you have a fair coin and you toss it until you have got equal number of heads and tails. What is the expected number of tosses? Note that probability that the game stops in odd number of tosses is 0. The probability that the game stops in 2 tosses = 0.5
Different solutions posted by Kalyan Parhi (EE IITB Alumnus), Abhash, Siva, Gaurav Sinha (CSE IITK 1996 Alumnus, Indian Revenue Service), Dinesh Krithivasan (IITM Alumnus, Phd University of Michigan, Senior Qualcomm Engineer) in comments!