Finding average speed given two velocities, help

[steph35]

Homework Statement

A person walks first at a constant speed of 47.0m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.10m/s

Homework Equations

What is her average speed over the entire trip?

The Attempt at a Solution

I tried (4.70m/s + 3.10m/s)/2 to get the average and got 3.9m/s but it was wrong...I can't really think of anything else b/c time isn't given...

 

[LowlyPion]

Homework Statement

A person walks first at a constant speed of 47.0m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.10m/s

Homework Equations

What is her average speed over the entire trip?

The Attempt at a Solution

I tried (4.70m/s + 3.10m/s)/2 to get the average and got 3.9m/s but it was wrong...I can't really think of anything else b/c time isn't given...

The average speed is the distance traveled divided by time.
Your answer is for equal time intervals at different speeds.
But you have unequal time intervals.
You need to find the total time that it took to go twice the AB distance.