Motion Word Problem

melanie0989

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Jun 22, 2015
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Two automobiles, A and B leave at same time and travel same route. Automobile A goes a rate of 55 miles per hour. Automobile B goes a rate of 40 miles per hour. How many hours after they begin the trip, will A be ahead of B?

The book says the answer is 4 hours. I'm not sure how to set up equation for that. I'm used to motion problems using the d=rt formula but there isn't even a distance to use in this problem.
 
Two automobiles, A and B leave at same time and travel same route. Automobile A goes a rate of 55 miles per hour. Automobile B goes a rate of 40 miles per hour. How many hours after they begin the trip, will A be ahead of B?
If they started at the same time from the same point taking the same route, then Auto A will be ahead of B for the entire route. So maybe some information is missing...?
 
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