<PRE><B>Question 991729</B>
An auto mobile driver traveled the first part of a 400 mile trip at an average rate of 50 miles per hour. Upon reaching an interstate rout, his average speed increased to 60 miles per hour. His total travel time was 7 hours. How far had he traveled when he reached the interstate route? 
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1st part DATA:
rate = 50 mph ; distance = x miles ; time = x/50 hrs
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2nd part DATA:
rate = 60 mph ; distance = 400-x miles ; time = (400-x)/60 hrs
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Equation:
time + time = 7 hrs
x/50 + (400-x)/60 = 7
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60x + 50(400-x) = 7*50*60
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10x + 20000 = 21000
10x = 1000
x = 100 miles (distance to the interstate)
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Cheers,
Stan H.
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