FILE No.199Unsolved
From 100 km apart, two trains start running toward each other, each at 50 km/h. A bird takes off from the front of one train at 80 km/h and heads for the other train. On arrival it immediately turns around, and keeps flying back and forth until the two trains meet.
What is the total distance the bird flew, in kilometers?
If you get stuck, open the hints one at a time, in order.
How many hours until the two trains meet?
The bird is flying the whole time.
Distance is speed times time.
What is the total distance the bird flew, in kilometers?
Choose the answer closest to the truth.
80 km
The answer is "80 km."
The trains approach each other at 50 km/h each, so it takes 1 hour to close the 100 km. The bird flies at 80 km/h the whole time, so it flies 80 km.
You do not need to count the number of round trips; you can get it from "time × speed."
Because you try to add up the distance of each trip one by one.
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