Question

when is the instantaneous speed same as the average speed

Answer 1

Heya Friend ☺

For happening instantaneous speed and the average speed is same there must be zero acceleration then there would be zero acceleration there will be no direction and speed

hope it helped you

Answer 2

Your question should be
When is instantaneous 'velocity' equal to average 'velocity'?
The answer is
When the acceleration of the body is zero, instantaneous velocity and average velocity are same. For acceleration to be zero there should be no chance in speed or direction.
Thanks.
Hope it helps you.