The disk with your favorite MP3 song, "Mahna Mahna" (https://www.mahnahmahna.net) on it has been scratched very badly. The disc was mixed up with three other scratched discs that were lying around. It is equally likely that any of the four discs holds "Mahna Mahna". A DJ friend of yours o ers to take a look since he claims to recover songs from any disc with a 50% chance(assuming the song is there). Given that he searches on disc 1 but cannot recover your song, what is the probability that your song is on disc i for i = 1; 2; 3; 4 ?