Question 508969
The boys were 3/8 of the way across a bridge when they heard the Cannonball Express approaching the bridge at 60 mph. They quickly calculated that they could just save themselvess by running to either end of the bridge at top speed. How fast could they run?
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This is a logic problem
When they heard the train they were 3/8 from the end where the train would come
It tells us the train would enter when they had run 3/8 the way. 
If they turned and ran the opposite way, there would be 3/8 + 3/8 = 6/8 or 3/4 across the bridge.
Therefore they will run the last 1/4 the length of the bridge, while the train travels the whole length the bridge. 
They must be running {{{1/4}}}*60 = 15 mph