Average velocity is different than average speed because calculating average velocity involves

Average velocity is different than average speed because calculating average velocity involves  considering the direction the bodies are moving.

When calculating average speeds you don't have to consider directions of the bodies.

This is because velocity is a vector quantity which must be defined by direction. Speed is a scalar quantity thus it does not have to be defined by direction.

Direction

Explanation:

Average speed is defined as the ratio o total distance covered to the total time taken. It is a scalar quantity and it's SI unit is m/s.

Average velocity is defined as thr ratio of total displacement covered to the total time taken. It is a vector quantity and it's SI unit is also m/s.

To calculate the average velocity we need direction also.