SOLUTION: At the same time Kris leaves Washington, D.C. for Detroit. Amy leaves Detroit for Washington, D.C.. The distance between the cities is 510 miles. Amy's average speed is 5 mph faste

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: At the same time Kris leaves Washington, D.C. for Detroit. Amy leaves Detroit for Washington, D.C.. The distance between the cities is 510 miles. Amy's average speed is 5 mph faste      Log On

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Question 504368: At the same time Kris leaves Washington, D.C. for Detroit. Amy leaves Detroit for Washington, D.C.. The distance between the cities is 510 miles. Amy's average speed is 5 mph faster than Kris's. How fast is Kris driving if they pass each others in 6 hours?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Kris x mph
Amy x+ 5 mph
..
They are moving towards each other

So add up their speed.

combined speed = x+ x + 5
( 2 x + 5 )
Time = 6 hours
Distance = 510 miles
Distance = speed * time
( 2 x +5 )* 6 = 510
12 x + 30 = 510
12 x = 510 + -30
12 x = 480
/ 12
x= 40 mph Kris
Amy 40 + 5 = 45 mph