Why was this downvoted? The math checks out. Multiplying by 4 and then dividing by 12 is wrong.
Easy way to verify this: assume only 1 person in the queue and only 1 machine. Then the original calculation yields 4/12 of a year, even though the actual wait time is (about) 1/12 of a year.
Easy way to verify this: assume only 1 person in the queue and only 1 machine. Then the original calculation yields 4/12 of a year, even though the actual wait time is (about) 1/12 of a year.