Suppose a four-year corporate bond provides a coupon of 6% per year payable semiannually and has a yield of 4% (semiannual compounding). The yield for all maturities on risk-free bonds is 3% per annum (semiannual compounding). Assume that defaults can take place every six months immediately before a coupon payment and the recovery rate is 30%. Estimate the default probabilities assuming : The default probabilities conditional on no earlier default are the same on each possible default date.