SOLUTION: at 10:30 A.M. two planes leave Houston, one flying east at 560 km/h and the other flying west at 640 km/h. At what time will they be 2100 km apart?

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Question 51627: at 10:30 A.M. two planes leave Houston, one flying east at 560 km/h and the other flying west at 640 km/h. At what time will they be 2100 km apart?
Answer by rchill(405) About Me  (Show Source):
You can put this solution on YOUR website!
Because the planes are flying in opposite directions, the equation becomes 560x%2B640x=2100 where x is the value in hours. Combining like terms produces 1200x=2100. Now divide both sides by 1200: 1200x%2F1200=2100%2F1200 which reduces to x=2100%2F1200. This simplifies to x=7%2F4 or 1.75 hours, which is the same as 1 hour 45 minutes.