Speed is the rate at which an object moves relative to its reference point. average speed is the total distance divided by the total time. we use average speed because the speed of an object may vary over time. common measures of speed include miles per hour, meters per second or kilometers per minute. if you drive at a speed limit of 65 miles per hour, it means that in one hour you will have traveled 65 miles from the reference point of where you began.

because the speed at which an object travels varies over time,
a
it is impossible to calculate any type of speed measurement.
b
distance is considered the more important measurement.
c
average speed is used, which is total distance divided by total time.
d
time is considered the more important measurement.