Robbie leaves his house and drives 5 miles North to the post office, 8 miles East to the park, 5 miles South to the grocery store, and then 8 miles West to get back home. What is Robbie's displacement?

Robbie's displacement is zero.

Explanation:

Displacement is called the change in position that a body experiences, from an initial point A, to an end point B, through movement. That is, displacement is understood as the length and direction that a body travels to move from an initial point to an end point. Displacement is a vector type quantity, which is described from the magnitude and the direction.

Only the start point and the end point are important for displacement. When the object ends at the same starting point, the displacement will be zero.

You know that Robbie leaves his house and drives 5 miles North to the post office, 8 miles East to the park, 5 miles South to the grocery store, and then 8 miles West to get back home.

Since in this case the start point and end point is Robbie's house, then the offset will be zero.