October 2015 was the forty-second consecutive month that the rate of inflation as measured by the personal

Question:

October 2015 was the forty-second consecutive month that the rate of inflation as measured by the personal consumption expenditures (PCE) price index was below the Federal Reserve's target of 2 percent.
a. Briefly explain why using the consumer price index (CPI) might yield a rate of inflation different from that found using the PCE price index.
b. Explain how the choice of the price index the Federal Reserve uses to measure inflation can affect monetary policy.