Two years ago, a company issued $20 million in long-term bonds at par value with a coupon rate of 9 percent. The company has decided to issue an addi- tional $20 million in bonds and expects the new issue to be priced at par value with a coupon rate of 7 percent. The company has no other debt outstanding and has a tax rate of 40 percent. To compute the company's weighted average cost of capital, the appropriate after-tax cost of debt is closest to:

答案是 4.2%.

說是用7%*(1-40%)

我想問為什麼在這個題目裏面用的是coupon rate來算cost of debt?

另外一道題是

Dot.Com has determined that it could issue $1,000 face value bonds with an 8 percent coupon paid semi-annually and a five-year maturity at $900 per bond. If Dot.Com's marginal tax rate is 38 percent, its after-tax cost of debt is closest to:
答案是先算出YTM,這個YTM是cost of debt..FV=$1,000;PMT=$40;N=10;PV=$900 Solve for i. The six-month yield, i, is 5.3149% YTM = 5.3149% × 2 = 10.62985% rd(1 − t) = 10.62985%(1 − 0.38) = 6.5905% 然後我就不懂了...Orz.為什麼上面那個用的是coupon rate.下面這個題目用的是YTM...