Julia G.
asked • 05/06/16When will the second train overtake the first?
A train leaves a station and travels east at 72 km/h. Three hours later, a second train leaves on a parallel track and travels east at 120 km/h. When will the second train overtake the first?
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1 Expert Answer
Jason B. answered • 05/06/16
Tutor
New to Wyzant
UDayton Grad, Current HS Math Teacher tutoring for Alg(p,1,2), Geom.
x = hrs traveled of first train
x-3 = hrs traveled of second train
When train 2 takes over (passes) train 1, they will have traveled equal distances. Therefore you set the two expressions of rate * time equal to each other.
72x = 120(x-3)
72x = 120x -360
-48x = -360
x = 7.5
72*7.5 =540=120*4.5
Train 2 will take over train 1 at 7.5 hours.
33 1.
Jason you made a mistake! Its actually 4.5 Hours, The answer is 72(t+3)=120t Explaining : The distance the trains have traveled will eventually be equal, we just don't know how long until, so it starts off as d1=d2, Train A has been traveling for an unknown amount of time (t) BUT we need to add the three hours that have elapsed when Train B takes off so train A's time is t + 3, and also its rate is 72 so it should be 72(t + 3). Train B has been traveling for an unknown amount of time so we put t and Train B's rate is 120, so the problem should be 72(t+3)=120t then you solve! (Check your answer key if you don't believe this is correct, because it should be correct)
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10/17/23
33 1.
im sorry if this comment is annoying.
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10/17/23
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33 1.
Jason I think you made a mistake! Its actually 4.5 Hours, The answer is 72(t+3)=120t Explaining : The distance the trains have traveled will eventually be equal, we just don't know how long until, so it starts off as d1=d2, Train A has been traveling for an unknown amount of time (t) BUT we need to add the three hours that have elapsed when Train B takes off so train A's time is t + 3, and also its rate is 72 so it should be 72(t + 3). Train B has been traveling for an unknown amount of time so we put t and Train B's rate is 120, so the problem should be 72(t+3)=120t then you solve! (Check your answer key if you don't believe this is correct, because it should be correct)10/17/23