Greg is in a bike race. at mile marker four (out of ten), his speed was measured at 13.5 mph.

which best describes the measured number?

it is the average speed of the bike rider.
it is the instantaneous speed of the bike rider.
it is the instantaneous velocity of the bike rider.
it is the average velocity of the bike rider.

Option C, It is the instantaneous velocity of the bike rider

Explanation:

Instantaneous velocity is the speed of an object at a given instant of time, location and in a certain direction. Instantaneous speed represents the magnitude part of the instantaneous velocity. Both instantaneous speed and velocity have same magnitude, but velocity  more specifically talk about location and direction in which speed is measured.  

Average speed or average velocity is derived by dividing total distance traveled by the time taken to travel the total distance. Since out of ten mile marker speed is measured at the fourth mile marker it will be considered as an instantaneous velocity  . It does not take into account the total distance traveled.

Hence, option C, is correct.

when it's short and dry.