Average speed = total distance covered/ total time taken
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Average velocity = change in distance/change in time
------So, after the subtraction to get average velocity, change in distance/change in time, there would be no difference in the two equations as to numerical ratio.
average speed = 1500 meters/60 seconds
average velocity = (1500 meters - 0 meters)/(120 seconds - 60 seconds)
Regardless of the numbers and even if the answer was variant there is no difference in numerical ration excepting the former, average speed uses totals, and the later, average velocity, uses changes.. The former, average speed, would graph as a line, while the latter, average velocity, would graph as a curve, but to get the average velocity you would draw a tangent ( a straight line ) to that curve.
So, these two concepts are rather interchangeable in simple mechanics.