You purchase a twenty year zero coupon bond with a yield of 5%. One year later you sell the bond at a yield of 4%. What is your rate-of-return?

25.94%

Explanation:

Assume, Face value of bond =$1000

Purchase price of twenty year zero coupon bond = 1000/((1+i)^N) . Where, yield = 5% =0.05 , N= number of years to maturity =20

==> Purchase Price = 1000/(1.05^20)

Purchase Price = 1000/2.65329770514

Purchase Price = $376.89

Selling Price after one year:  1000/(1+I)^19. Where i=yield=4%=0.04, N=19

Selling Price=1000/(1.04^19)

Selling Price = 1000/2.10684917599

Selling Price = $474.64

Rate of Return = (474.64/376.89) - 1

Rate of Return = 1.25935949481281 - 1

Rate of Return = 0.2594

Rate of Return = 25.94%