Answer:
To find the unit rate describing the number of seconds it takes the marble to travel one centimeter, we need to invert the given unit rate of 2 centimeters per second. Inverting the unit rate means swapping the numerator and denominator of the fraction to get a new fraction with the same value but different units.
2 centimeters/second = 1/2 seconds/centimeter
Therefore, the unit rate describing the number of seconds it takes the marble to travel one centimeter is 1/2 seconds/centimeter. This means that it takes the marble half a second to travel one centimeter.