How do you find magnitude of average velocity

Here's the problem:
A runner runs in the 400m track and completes it in 3mins. Find the magnitude of her average velocity.

What does the 2nd sentence mean? I've only just started learning physics so I would be grateful if someone could explain all of this to me.

"Magnitude" means without regard to direction. Average velocity is a vector quantity, meaning it has both an amount (magnitude) and a direction. This question is just asking for the amount.

Averge velocity is defined as the displacement (change in position) divided by the time required. The 400 m race is once around an oval track. Therefore, the runner ends at the same place they started, and the change in position is zero. So, the displacement is zero, and the average velocity is zero. And that's just a magnitude already, since an average velocity of zero has no direction.

The answers before mine have answered a different question, "What is the average speed?". Average speed is not a vector quantity, so it wouldn't make sense to ask about its magnitude, anyway.

You're welcome. I'm glad I could help.

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The second sentence simply means what is her total average velocity. You'll find some questions will start asking for, "in what direction..." as well. In those cases, you will find the magnitude of velocity, acceleration, etc. as well as find a direction.
So in this problem, don't over complicate it. A lot of times in physics you will get questions that will sound really confusing, but in reality, they are very straight forward.

So here, we know the runner moves a distance of 400m, and she does this in 3 min.
Velocity is simply a distance traveled over a certain time. So let's put two and two together.

Her average velocity here will be 400m per 3min. (400m/3min)