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Two trains start at the same moment from stations that are 300 miles apart and travel toward each other on parallel tracks. One train travels at 50 miles per hour and the other at 70 miles per hour. How many hours after they start do the two trains pass each other?
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Correct answer
B
When two objects move toward each other, the gap between them shrinks at the sum of their speeds. Closing speed = 50 + 70 = 120 mph. Time to close the 300-mile gap = 300 ÷ 120 = 2.5 hours.
Common errors: averaging the two speeds to 60 and computing 300 ÷ 60 = 5, or using only the slower train's speed for 300 ÷ 50 = 6, both ignore that the gap closes at the speeds combined.
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