When is the instantaneous velocity equal to avg velocity?

Mainly, when the velocity doesn't change. Also, in the case of
varying velocity, the instantaneous velocity might, for a brief
instant, be equal to the average velocity.

At a small time interval, the average velocity is approximately equal to the instantaneous velocity. However, the values of the average velocity and the instantaneous velocity approach each other , as the length of the time interval is decreased more and more.

When there is no acceleration or when there is constant acceleration. When either of these cases is present, the graph of velocity versus time will be linear. When there is linear velocity, the average velocity will equal the instantaneous velocity at any point on the graph.

When an object is in constant motion (when there is no acceleration). At any point in that motion the average and instantaneous velocities will be the same.

That is the case when you are talking about instantaneous speed and velocity - or when the velocity is constant. In the case of an average speed and velocity, this relation does not hold.

If the velocity is constant (i.e., there is no acceleration). Terminal velocity is an example, although any constant velocity would fit this description.

The tangent at a point on the position-time graph represents the instantaneous velocity. 1. The tangent is the instantaneous slope. 2. Rather than "average" velocity, the slope gives you "instantaneous" velocity. The average of the instantaneous gives you average velocity.

Average velocity is the average of the velocty of entire motion where as instantaneous velocity is the velocity at an instant, it may be a function of time or displacement.