Question 1120830
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Train #12 travels for 12 minutes (1/5 hour) at 55mph before train #7 starts; the distance train #12 travels in that time is (1/5)(55) = 11 miles.  So when train #7 starts, the trains are 16-11 = 5 miles apart.<br>
The combined speeds of the two trains is 100mph; together to travel those 5 miles requires 5/100 = 1/20 hour, or 3 minutes.<br>
So the trains meet when train #12 has been traveling for 12+3 = 15 minutes and train #7 has been traveling for 3 minutes.<br>
The ratio of the speeds of the two trains is 55:45 or 11:9, so train #12 travels 11/20 of those 5 miles and train #7 travels 9/20 of the 5 miles.  11/20 of 5 miles is 2.75 miles; so when the trains meet train #12 has traveled 11+2.75=13.75 miles.<br>
Answers: When the trains pass, train #12 is 13.75 miles from its starting point at the downtown station, and it has been traveling for 15 minutes.