Hiking the hill

Sarah's average speed for a journey was 2 mph, and her return average speed was 4 mph. What is her average speed for the whole journey?
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Problem



Sarah walks uphill at an average of 2 miles per hour, and downhill at an average of 4 miles per hour.

She goes for a 6 mile hike up a hill, and then returns downhill by the same route.

What is Sarah's average speed for the whole journey?

 

 

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.