Joe moved to NYC last year and lives right by a subway line. There are two nice parks close by, which are also right by the same subway line, one north and the other south of Joe's apartment. Since Joe likes both parks equally, every Sunday morning he just walks to the subway station at a random time and takes whichever train comes first. I.e., if northbound train comes first, Joe will hop on and go to the north park that Sunday; if the southbound train comes first, he will go to south park that Sunday. Both northbound and southbound trains run at a regular interval of once every 10 minutes. After a year, to his puzzlement, Joe noticed on average he ended up in the north park 9 times out of 10 Sundays. Could you provide him with an explanation? (BTW, if your first thought is that Joe didn't leave his apartment randomly, then please be assured that it is indeed the case the Joe leaves at random time. In other words, that first thought is NOT the correct explanation.)