SOLUTION: 2nd question (and last) that I am helping my daughter with...I can not seem to place enough information into this to solve. Two joggers were crossing a railroad bridge when they

Question 124087: 2nd question (and last) that I am helping my daughter with...I can not seem to place enough information into this to solve.
Two joggers were crossing a railroad bridge when they suddenly heard the sound of an approachin train. they were smart enough to run for safety -- but each one ran in the opposite direction. Happily, each jogger reached his perspective end of the bridge in time to avoid the train.
If they wer 2/5 of the way across the bridge when they heard the train and the train was going 50mph and they both ran at the same speed how fast did the two gys run in miles per hour??
So the guy running toward the train gets off and the train then proceeds down the length of the bridge and the other guy gets off. The 2nd guy then has 1/5 left as the train crosses this bridge of unknown length. is it 1/5th of the speed??
Distance is equal to rate/time. Or do I need the speed of sound factored in??
Answer by PBMathandscience(9) (Show Source): You can put this solution on YOUR website!
They were 2/5 of the way down the bridge when they heard the train. Assume that the train was coming from behind (otherwise this doesn't work). Also assume that each jogger barely escapes. The train is traveling 50 mph.
Let the length of the bridge be L. Let the speed of the joggers be S.
When the jogger that runs toward the short end of the bridge, and towards the train, reaches the end, he has travelled .4L. The other jogger has, at the same time, reached a point at .8L. (He started at .4L, and runs the same speed as the other jogger).
The second jogger need to cover the remaining .2L before he is run over by the train, which has now started onto the bridge (since it just missed the first jogger). The train is traveling at 50 mph. The train will cover the length of the bridge in L/50 hours. So,

Divide both sides of the equation by L, and multiply both sides by 50:

Simplify:

Multiply both sides by S

They were running at 10 mph.
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