1. Why is the t-bill’s return independent of the state of the economy? Do t-bills promise a completely risk-free return?
Answer: The 8 percent t-bill return does not depend on the state of the economy because the treasury must (and will) redeem the bills at par regardless of the state of the economy.
The t-bills are risk-free in the default risk sense because the 8 percent return will be realized in all possible economic states. However, remember that this return is composed of the real risk-free rate, say 3 percent, plus an inflation premium, say 5 percent. Since there is uncertainty about inflation, it is unlikely that the realized real rate of return would equal the expected 3 percent. For example, if inflation averaged 6 percent over the year, then the realized real return would only be 8% - 6% = 2%, not the expected 3%. Thus, in terms of purchasing power, t-bills are not riskless.
Also, if you invested in a portfolio of T-bills, and rates then declined, your nominal income would fall; that is, t-bills are exposed to reinvestment rate risk. So, we conclude that there are no truly risk free securities in the United States. If the treasury sold inflation-indexed, tax-exempt bonds, they would be truly riskless, but all actual securities are exposed to some type of risk.