Bunuel wrote:
Two trains are heading toward each other on a 750-kilometer straight track. One train is heading due east at 70 kilometers per hour and the other train is heading due west at 80 kilometers per hour. How much time do the conductors have before the trains collide?
A. 3 hours
B. 4 hours
C. 5 hours
D. 9 hours
E. 11 hours
Since the trains are heading toward each other, we can let the time when the two trains would meet be t. Since distance = rate x time, the distance of the train heading east is 70t and the distance of the train heading west is 80t.
Now we can determine t:
distance of 1st train + distance of 2nd train = total distance
70t + 80t = 750
150t = 750
t = 5 hours
Alternate Answer:
Since one train travels 70 km an hour and the other travels 80 km an hour, the distance between the trains decreases 70 + 80 = 150 km every hour. Since they were 750 km apart, there will be 750/150 = 5 hours for the conductors to stop them before they collide.
Answer: C
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