The sum of the frictional and structural unemployment rates is equal to the a. potential unemployment rate. b. actual unemployment rate. c. cyclical unemployment rate. d. full employment rate.

Frictional unemployment occurs when workers move between jobs voluntarily, taking some time to find a new job that better suits their skills. Structural unemployment occurs when there is a mismatch between the skills possessed by workers and the skills required for available jobs, usually due to changes in the economy. Cyclical unemployment is related to fluctuations in the economy, such as recessions or expansions, causing a change in the demand for labor. Lastly, the actual unemployment rate represents the total percentage of people in the labor force who are unemployed, while the potential unemployment rate refers to the unemployment rate that would occur if the economy was operating at its full potential. The full employment rate, on the other hand, represents the percentage of the labor force employed when the economy is operating at its peak.

Let's look at each option and understand how they relate to our given information about the sum of frictional and structural unemployment rates. a. Potential unemployment rate: The potential unemployment rate would include frictional, structural, and cyclical unemployment. Since the question states the sum is only for frictional and structural unemployment, this option cannot be correct. b. Actual unemployment rate: The actual unemployment rate includes all three types of unemployment: frictional, structural, and cyclical. However, our given information only mentions the sum of frictional and structural unemployment rates, so this option is also not correct. c. Cyclical unemployment rate: Cyclical unemployment is a separate type of unemployment and is not related to the sum of frictional and structural unemployment rates, making this option incorrect. d. Full employment rate: Full employment occurs when the economy is operating at its peak, and there are only frictional and structural unemployment rates, as cyclical unemployment is not present. This means that the sum of frictional and structural unemployment rates would be equal to the full employment rate.

Based on our analysis of the options, the correct answer is: d. Full employment rate.