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T _ N N _ L Clue
TWO MINUTES. IT TAKES THE FRONT OF THE TRAIN ONE MINUTE AND THE REST OF THE TRAIN WILL TAKE TWO MINUTES TO CLEAR THE TUNNEL 25 KILOMETERS. THE PLANES ARE TRAVELING AT A COMBINED SPEED OF 25 KILOMETERS PER MINUTE. SO THEY WILL BE 25 KILOMETERS APART ONE MINUTE BEFORE THEY MEET. THE INITIAL DISTANCE BETWEEN THE PLANES IS IRRELEVANT FOR THE TRAIN TO PASS COMPLETELY THROUGH THE TUNNEL, IT MUST TRAVEL 2 MILES. AFTER 1 MILE TRAVEL, THE TRAIN WOULD BE COMPLETELY IN THE TUNNEL, AND AFTER ANOTHER MILE IT WOULD BE COMPLETELY OUT AND SINCE THE TRAIN IS TRAVELING AT 1 MILE A MINUTE, IT WILL TAKE 2 MINUTES TO PASS THROUGH THE TUNNEL THE FLY WOULD HAVE TRAVELLED 90 MILES. THE TRAINS ARE 100 MILES APART, AND THE TRAINS ARE TRAVELLING TOWARD EACH OTHER AT 40 AND 60 MPH, THE TRAINS WILL MEET IN ONE HOUR. THE FLY WILL HAVE BEEN FLYING FOR AN HOUR AT 90 MPH AT THAT POINT, SO THE FLY WILL HAVE TRAVELLED 90 MILES