sara walks part way around a swimming pool. she walks 50 yards north, then 20 yards

+20 yards

Explanation:

Given:

North = 50 yards

East = 20 yards

South = 50 yards

Required

Calculate the magnitude of displacement

Displacement is a vector quantity and it is a measure of distance taken and the direction of the distance.

Take up directions as positive and down directions as negative.

Similarly, we'll take right direction as positive and left direction as negative.

We understand that;

North is upwards; so, the displacement is +50 yards

East is rightwards; so, the displacement is +20 yards

South is downwards; so the displacement is -50 yards

Hence, her total displacement is

Displacement = +50 yards + 20 yards - 50 yards

Displacement = +20 yards

Hence, Sara's displacement is +20 yards