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Author:  Gennadiy [ Fri Jul 22, 2011 2:40 pm ]
Post subject:  GMAT Speed / Distance / Time

Alex leaves Atlanta heading directly toward Philadelphia at 8:00 a.m., traveling at 50 miles per hour. Heidi leaves Philadelphia, 600 miles away, heading directly for Atlanta at the same time, traveling at 70 miles per hour. At what time will they pass each other?

A. 1 p.m.
B. 2 p.m.
C. 2:45 p.m.
D. 3 p.m.
E. 3:30 p.m.

1) The distance between Atlanta and Philadelphia is 600 miles.

2) Heidi starts in Philadelphia and Alex starts in Atlanta, both at the same time, 8:00 a.m. Alex travels at 50 miles per hour, while Heidi travels at 70 miles per hour.

3) After T hours they met. The formula for distance is speed × time = distance. Therefore Alex drove 50T miles, while Heidi traveled 70T miles.

4) The sum of the distances they travelled is the whole distance between Atlanta and Philadelphia. So we have the following equation:
50T + 70T = 600
120T = 600
T = 5

5) 8:00 a.m. + 5 hours = 1:00 p.m.