At the same time Kris leaves Washington DCfor DetroitMichiga

At the same time Kris leaves Washington D.C.,for Detroit,Michigan,Amy leaves Detroit for Washington D.C. The distance between the cites is 510 miles.Amy\'s average speed is 5 miles per hour faster than Kris\'s. How fast is Kris\'s average speed if they pass each other in 6 hours?

Solution

Kris DATA:
time = 6 hrs ; distance = x miles ; rate= d/r = x/6 mph
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Amy DATA:
time = 6 hrs ; distance = \"510-x\" miles ; rate = d/r = (510-x)/6
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EQUATION:
Amy rate - Rick rate = 5 mph
(510-x)/6 - x/6 = 5
510-x - x = 30
-2x=-480
x=240 miles (Kris\'s distance)
Kris\'s rate = 240/6 = 40 mph