if a car averages 55 mph on a certain trip it will arrive 2

if a car averages 55 mph on a certain trip, it will arrive 2 hours early. If the car averages 35 mph it will arrive 2 hours late. How many miles is the trip?

Solution

1st car DATA:
rate = 55 mph ; distance = x miles ; time = d/r = x/55 hrs
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2nd car DATA:
rate = 35 mph ; distance = x miles ; time = d/r = x/35 hrs
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Equation:
slower time - faster time = 4 hrs
x/35 - x/55 = 4
55x - 35x = 4*35*55
20x = 7700
x = 385 miles (length of the trip)