SOLUTION: Two trains approach one another along (straight) parallel tracks. They start out at the same time from stations 90 km apart. One train travels at 100 km per hour, the second train

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Question 575097: Two trains approach one another along (straight) parallel tracks. They start out at the same time from stations 90 km apart. One train travels at 100 km per hour, the second train at 80 km per hour. How far has the faster train gone when they pass each other?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You can think of one train as standing still and
the other approaching at the sum of their speeds.
I will say the slower one is standing still.
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The faster one approaches at +100+%2B+80+=+180+ km/hr
+90+=+180t+
+t+=+.5+ hrs
They meet in a half hour
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Now, switching back to the original situation:
Equation for faster train:
+d%5B1%5D+=+100t+
+d%5B1%5D+=+100%2A.5+
+d%5B1%5D+=+50+
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Equation for the slower train:
+d%5B2%5D+=+80%2At+
+d%5B2%5D+=+80%2A.5+
+d%5B2%5D+=+40+
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The faster train has gone 50 km when they meet