SOLUTION: A motorist travels travels 400 km partly at 100 km/hr and partly at 80 km/h. If he had traveled at 80 kn/hr instead of 100 km/hr and had 100 km/h instead of 80 km/hr, the journey w
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Question 1129074: A motorist travels travels 400 km partly at 100 km/hr and partly at 80 km/h. If he had traveled at 80 kn/hr instead of 100 km/hr and had 100 km/h instead of 80 km/hr, the journey would have taken 0.5 h longer. find his time for the trip.
Answer by greenestamps(13198) (Show Source): You can put this solution on YOUR website!
Let the distances (km) for the two parts of the trip be x and 400-x. Then
The total number of hours for the trip, at 100km/hr for the first part and 80km/hr for the second, was
If the two speeds had been switched, the total number of hours would have been
The second trip would have taken 0.5 hours longer:
Multiply through by the LCM, 400:
Solve....
He traveled at 100km/hr for 300 km (3 hours) and at 80 km/hr for 100 km (1.25 hours); total time 4.25 hours.
If the speeds had been switched, he would have traveled at 80km/hr for 300 km (3.75 hours) and 100km at 100km/hr (1 hour); total time 4.75 hours.
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