Question 274022
Heather is standing on a railroad bridge.
 A train is approaching from the direction shown by the yellow arrow (right).
 If Heather runs at a speed of 10mph towards the train, she will reach point P (300 ft away to the left of her) at the same moment that the train does. 
If she runs to point Q (500 ft to her right) at the other end of the bridge at the speed of 10mph, she will reach point Q also at the same moment that the train does.
 How fast, in mph, is the train traveling? 
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This is a thought problem, not much math is needed. 
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We know that the train is at the beginning of bridge when H has run 300 ft.
Another words when H has runs 300 ft towards the right end, at that moment
the train enters the bridge, H has another 200 ft to the right end of the bridge
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we can say, H runs 200 ft while the train covers 800 ft (length of the bridge)
Using a ratio equation where s = speed of the train
{{{s/10}}} = {{{800/200}}}
or
{{{s/10}}} = {{{4/1}}}
s = 40 mph is the train
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Did I say this well enough to make sense to you??