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S P _ _ D Clue
THE TRAIN IS MOVING AT 40 MILES PER HOUR. IMAGINE THAT A FRIEND IS WALKING WITH YOU. WHEN THE TRAIN WHISTLE BLOWS, YOU HEAD AWAY FROM THE TRAIN, HE HEADS TOWARD IT. WHEN HE REACHES SAFETY, YOU WILL BE 6/8 (OR 3/4)OF THE WAY ACROSS THE BRIDGE, AND THE TRAIN WILL HAVE JUST REACHED THE BRIDGE. FOR THE TRAIN TO CROSS 4/4 OF THE BRIDGE IN THE TIME YOU CROSS THE REMAINING 1/4, THE TRAIN MUST BE MOVING FOUR TIMES YOUR SPEED THE TRAIN IS ABOUT TO LEAVE AND YOU WILL NOT BE ABLE TO CATCH THE TRAIN. THE AMOUNT OF TIME TAKEN TO TRAVEL TO THE HALFWAY POINT AT 15 MILES AN HOUR IS THE SAME AMOUNT OF TIME TAKEN TO REACH THE TRAIN STATION WHEN TRAVELLING TO THE RAILROAD STATION AT 30 MILES AN HOUR. FOR EXAMPLE, LET'S ASSUME THAT THE DISTANCE TO TRAVEL IS 30 MILES. WHEN TRAVELLING AT 30 MILES AN HOUR, IT TAKES 1 HOUR. WHEN TRAVELLING AT 15 MILES AN HOUR, IT WILL ALREADY TAKE 1 HOUR TO REACH THE HALFWAY POINT KOLKHOZ IS 120 MILES AWAY FROM THE CITY AND THE TRUCK SHOULD TRAVEL AT 24 MILES AN HOUR. AT 30 MILES PER HOUR A TRUCK TRAVELS A MILE IN 2 MINUTES; AT 20 MILES PER HOUR, IN 3 MINUTES. AT THE LATTER SPEED THE TRUCK IS 1 MINUTE SLOWER PER MILE. TO LOSE 2 HOURS, OR 120 MINUTES, TAKES 120 MILES, WHICH IS HOW FAR THE KOLHOZ IS FROM THE CITY. AT 30 MPH, THE TRUCK WOULD COVER 120 MILES IN 4 HOURS. THE TRIP IS TO TAKE 1 HOUR LONGER, OR TO ARRIVE AT 11:00 A.M., AND CALLS FOR A SPEED OF 24 (120/5) MILES PER HOUR 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