How heavy is the average train?

At 10 a.m., a freight train leaves Chicago for Denver traveling at an average speed of 60 mph.2 hours later, a high speed passenger train leaves Chicago for Denver traveling at an average speed of 150 mph. Write equation how many hours will fast one pass?

• Answer:

  Let "d" = distance in miles traveled by the two trains; let "t" = the time in hours traveled by the faster train, which is what you're looking for. You want to find where "d" is the same for both trains, which is the point at which the faster train overtakes the slower. So what you want is two simple equations showing that distance: 60 (t + 2) = d and 150t = d Therefore, 150t = 60 (t+2) or 150t = 60t + 120 combining like terms 90t = 120 t = 1.33333 (1-1/3 hours), or 1 hour and 20 minutes Now show the proof of that.