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Bob, driving a new Ford, travels 330 miles in the same amount of time it takes John, driving an old Chevy and traveling 10 miles per hour faster, to travel 390 miles. How fast is Bob driving?

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sqdancefan

Answer:

  55 mph

Step-by-step explanation:

Let x represent Bob's speed. Then John's speed is x+10, and their respective times are found by ...

  time = distance/speed

  330/x = 390/(x+10) . . . . . . . the times are the same

  330(x +10) = 390x . . . . . . .  multiply by x(x+10)

  3300 = 60x . . . . . . . . . . . . . subtract 330x

  55 = x . . . . . . . . . . . . . . . . . . divide by the coefficient of x

Bob is driving at 55 miles per hour.

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