Question 779276
1. Starting at noon. John drives north along a highway at a speed of 70 mi/hr until 2:30pm.
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So at 2:30pm he has traveled 70 mi/hr for 2.5 hours. 
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How far has he traveled since noon? 
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Since distance = speed×time, at 2:30pm, he has traveled 70×2.5 = 175 miles.
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2. He then continues in the same direction at a different steady speed for a distance of 75 miles until 4:00 pm. 
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So he goes 75 miles from 2:30 to 4:00pm, which is 1.5 hours.
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What is his speed between 2:30 pm and 4:00pm?
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since speed = distance/time, his speed is 75/1.5 = 50 mi/hr  
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3. From 4:00 pm he travels an additional 180 miles in the same direction to arrive 
at his destination. He travels this final part of his journey at a constant speed of 60 mi/hr. 
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So he travels 180 miles at 60 mi/hr,
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When does he get to his destination? 
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Since time = distance/speed, 180/60 = 3 hours after 4:00pm or 7:00pm 
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4. What is John's average speed between his start at noon and the time he arrives at his destination?
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In part 1, he drives 175 miles.
In part 2, he drives 75 miles.
In part 3, he drives 180 miles.

So he drives a total of 175+75+180 or 430 miles
From noon to 7:00 is 7 hours.

Average speed = total distance/total time = 430/7 = 61 3/7 mi/hr.

Edwin</pre>