How do I find the average speed for this problem?

AI Thread Summary
To find Julie's average speed to her grandmother's house, first calculate the time taken for each half of the journey. She drives 50 miles at 42 mi/hr, taking approximately 1.19 hours, and 50 miles at 68 mi/hr, taking about 0.74 hours. Adding these times gives a total travel time of approximately 1.93 hours. The average speed is then calculated by dividing the total distance of 100 miles by the total time of 1.93 hours, resulting in an average speed of about 51.8 mi/hr. This method ensures an accurate calculation of average speed without common pitfalls.
ixerr
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Homework Statement


I don't know how to start.. someone please give me a step-by-step explanation.
Julie drives 100 mi to Grandmother's house. On the way there she drives half of the distance at 42 mi/hr and half the distance at 68 mi/hr. What is Julie's average speed (in mi/hr) on the way to Grandmother's house?


Homework Equations





The Attempt at a Solution

 
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You know the total distance, so you need to work out the total time taken. To do this, work out the travel time on each different section, and then add them up.

If you do it this way, you'll avoid falling into the trap ! :smile:
 

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