SOLUTION: Two trains traveling on parallel tracks are going toward each other from a distance of 960 kilometers. if one train moving at 100 kilometers per hour and the other is moving at 140

Question 186649: Two trains traveling on parallel tracks are going toward each other from a distance of 960 kilometers. if one train moving at 100 kilometers per hour and the other is moving at 140 kilometers per hour, after how many hours will the trains pass each other?
Answer by Edwin McCravy(20060) (Show Source): You can put this solution on YOUR website!
Two trains traveling on parallel tracks are going toward each other from a distance of 960 kilometers. if one train moving at 100 kilometers per hour and the other is moving at 140 kilometers per hour, after how many hours will the trains pass each other?



Their approach rate is 100+140 or 240 km/h and 960/240 = 4 hours.

But here is the way to do it with algebra.  Make this chart:

               RATE    TIME    DISTANCE
Slower train    
Faster train   

Put in the rates and t for the time until they pass:

               RATE    TIME    DISTANCE
Slower train    100     t 
Faster train    140     t

Then use DISTANCE = RATE x TIME to fill in the distances

               RATE    TIME    DISTANCE
Slower train    100     t        100t
Faster train    140     t        140t

The the sum of their distances traveled must equal the
960 km they were at the start, so the equation is

Slower train's distance traveled to point of passing

      + 

          Faster train's distance to point of passing

              =

                   960 km.

100t + 140t = 960

Solve that and get 4 hours.

Edwin

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