SOLUTION: Sue travels an average driving speed of 20km/h faster than john. she can drive 810km in the same time john can drive 720km. what is each of there speed in km/h and time in h

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Question 1173788: Sue travels an average driving speed of 20km/h faster than john. she can drive 810km in the same time john can drive 720km. what is each of there speed in km/h and time in h
Answer by ikleyn(52855) About Me  (Show Source):
You can put this solution on YOUR website!
.

Let x = John' speed, in km/h.


Then the Sue speed is (x+20) km/h.


From the condition, you have this "time" equation


    810%2F%28x%2B20%29 = 720%2Fx,


or, dividing by 90 both sides


    9%2F%28x%2B20%29 = 8%2Fx.


Cross multiply

    9x = 8(x+20)


and solve

    9x = 8x + 160

    9x - 8x = 160

       x    = 160  km/h for John,

and           160+20 = 180 km/h for Sue.

Solved.