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.

it is the instantaneous speed of the bike rider.

Explanation:

First of all, let's remind the difference between speed and velocity:

- speed is a scalar, and it is the ratio between the distance covered and the time taken:

- velocity is a vector, which consists of a magnitude (the speed) and a direction as well.

The term 'instantaneous' means that the speed (or velocity) is measured at one precise instant of time, while the term 'average' means it is measured over a longer time period.

Based on all these definitions above, we can conclude that the correct answer is

it is the instantaneous speed of the bike rider.

Because in this problem, only the speed is given (no direction), so this is not a velocity, and also it is measured at one precise instant of time, so it is an instantaneous speed.