Answer:
after 6 hours 15 minutes, they will meet at a point 187.5 miles from train B's start
Explanation:
Assuming the trains are traveling toward each other, they are closing the gap at the rate of 50+30 = 80 miles per hour. Then there will be no gap left after ...
(500 mi)/(80 mi/h) = 25/4 h = 6.25 h . . . time until trains meet
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In that time, Train A will have traveled ...
(50 mi/h)(6.25 h) = 312.5 mi . . . . distance from A's start
and Train B will have traveled ...
(30 mi/h)(6.25 h) = 187.5 mi . . . . distance from B's start
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The B will reach A at a point 3/8 of the distance from B to A, 187.5 mi from B's start.