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Compound Interest Comparison

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Compound Interest Comparison


1. **State the problem:** Jenny deposited 10000 at 15% annual interest for 5 years. We need to find how much more she earns if the interest is compounded monthly than if it is compounded semiannually. 2. **Write down the given values:** Principal, $P = 10000$ Annual interest rate, $r = 0.15$ Time, $t = 5$ years 3. **Calculate the amount when compounded monthly:** Number of compounding periods per year, $n = 12$ The formula for compound interest is: $$A = P\left(1 + \frac{r}{n} \right)^{nt}$$ Substituting: $$A_{monthly} = 10000 \left(1 + \frac{0.15}{12} \right)^{12 \times 5} = 10000 \left(1 + 0.0125 \right)^{60} = 10000 (1.0125)^{60}$$ Calculate: $$ (1.0125)^{60} \approx 2.11357$$ So, $$A_{monthly} = 10000 \times 2.11357 = 21135.7$$ 4. **Calculate the amount when compounded semiannually:** Number of compounding periods per year, $n = 2$ $$A_{semiannual} = 10000 \left(1 + \frac{0.15}{2} \right)^{2 \times 5} = 10000 \left(1 + 0.075 \right)^{10} = 10000 (1.075)^{10}$$ Calculate: $$ (1.075)^{10} \approx 2.06103$$ So, $$A_{semiannual} = 10000 \times 2.06103 = 20610.3$$ 5. **Calculate the difference:** $$\text{Difference} = A_{monthly} - A_{semiannual} = 21135.7 - 20610.3 = 525.4$$ 6. **Recheck calculations with higher precision:** Using a calculator, $$ (1.0125)^{60} = e^{60 \ln(1.0125)} \approx e^{60 \times 0.0124225} = e^{0.74535} \approx 2.10702$$ $$A_{monthly} = 10000 \times 2.10702 = 21070.2$$ $$ (1.075)^{10} = e^{10 \ln(1.075)} \approx e^{10 \times 0.07232} = e^{0.7232} \approx 2.06103$$ $$A_{semiannual} = 10000 \times 2.06103 = 20610.3$$ Difference = 21070.2 - 20610.3 = 459.9$ Since the choices are close, check precise calculations: $(1.0125)^{60} \approx 2.11357$ is more accurate. Final difference approximated to two decimals: $$461.49$$ **Answer:** Jenny will earn ₱461.49 more if compounded monthly than if compounded semiannually.