Question 258220
A car takes 2 hours to travel between two cities. If the average speed decreases 20km/hr it will take 30 minutes more. What is the distance between the two cities. 
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Original DATA:
time = 2 hrs. ; distance = x km ; rate = d/t = x/2 kph
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New DATA:
time = 2.5 hrs ; distance = x km ; rate = d/t == x/2.5 kph
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Equations:
original speed - new speed = 20 kph
(x/2) - (x/2.5) = 20
(2.5x - 2x)/(2*2.5) = 20
0.5x = 100
x = 200 km (distance between the two cities.
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Cheers,
Stan H.