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| rev | Admin | (Created page with "'''Solution: E''' From basic principles, the accumulated values after 20 and 40 years are <math display="block"> \begin{align*} 100[(1+i)^{20}+(1+i)^{16}+\cdots+(1+i)^{4}]=100\frac{(1+i)^{4}-(1+i)^{24}}{1-(1+i)^{4}} \\ 100[(1+i)^{40}+(1+i)^{36}+\cdots+(1+i)^{4}]=100{\frac{(1+i)^{4}-(1+i)^{44}}{1-(1+i)^{4}}} \end{align*} </math> The ratio is 5, and thus (setting <math>x=(1+i)^4</math>)) <math display="block"> \begin{array}{l}{{5=\frac{(1+i)^{4}-(1+i)^{44}}{(1+i)^{4}-(...") | Nov 17'23 at 21:46 | +821 |