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Question 5.1: A savings bank is selling long-term savings certificates tha......

A savings bank is selling long-term savings certificates that pay interest at the rate of 7\frac{1}{2}% per year, compounded continuously. The bank claims that the actual annual yield of these certificates is 7.79%. What does this mean?

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The nominal interest rate is 7\frac{1}{2}%. Since the interest is compounded continuously, the effective annual interest rate is given by (5.1) as

i  =  \underset{m→∞}{\lim}\left[\left(1  +  \frac{r}{m}\right)^m  –  1\right]  =  e^r  –  1  (5.1)

i = e^{0.075} – 1 = 0.077884 ≈ 7.79%

Formula (5.1) is very convenient, provided a calculator is available to carry out the exponentiation. Tabulated values of the effective annual interest rate may be used instead; see Appendix B.

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