Question: WHICH WOULD YOU CHOOSE?
Deposit ₱1,500 at the end
of every month into an
account earning 6%
annual interest
compounded monthly for
2 years.
Deposit ₱2,500 at the end
of every month into an
account earning 4%
annual interest
compounded monthly for
1.5 years.
LC 2: Determine the accumulated value of
investments over time using sequences and
series.
1. **State the problem:**
We want to find the accumulated value of two different monthly deposit investments with compound interest.
2. **Formula used:**
The future value of an ordinary annuity (deposits at the end of each period) compounded monthly is given by:
$$ A = P \times \frac{(1 + r)^n - 1}{r} $$
where:
- $A$ is the accumulated amount
- $P$ is the monthly deposit
- $r$ is the monthly interest rate (annual rate divided by 12)
- $n$ is the total number of deposits (months)
3. **Calculate for the first investment:**
- $P = 1500$
- Annual interest rate = 6%, so monthly rate $r = \frac{6}{100 \times 12} = 0.005$
- Time = 2 years, so $n = 2 \times 12 = 24$
Calculate:
$$ A_1 = 1500 \times \frac{(1 + 0.005)^{24} - 1}{0.005} $$
Calculate $(1 + 0.005)^{24}$:
$$ (1.005)^{24} \approx 1.12749 $$
So:
$$ A_1 = 1500 \times \frac{1.12749 - 1}{0.005} = 1500 \times \frac{0.12749}{0.005} $$
Simplify fraction:
$$ \frac{0.12749}{0.005} = 25.498 $$
Therefore:
$$ A_1 = 1500 \times 25.498 = 38247 $$
4. **Calculate for the second investment:**
- $P = 2500$
- Annual interest rate = 4%, so monthly rate $r = \frac{4}{100 \times 12} = 0.0033333$
- Time = 1.5 years, so $n = 1.5 \times 12 = 18$
Calculate:
$$ A_2 = 2500 \times \frac{(1 + 0.0033333)^{18} - 1}{0.0033333} $$
Calculate $(1 + 0.0033333)^{18}$:
$$ (1.0033333)^{18} \approx 1.06168 $$
So:
$$ A_2 = 2500 \times \frac{1.06168 - 1}{0.0033333} = 2500 \times \frac{0.06168}{0.0033333} $$
Simplify fraction:
$$ \frac{0.06168}{0.0033333} = 18.504 $$
Therefore:
$$ A_2 = 2500 \times 18.504 = 46260 $$
5. **Conclusion:**
- The accumulated value of the first investment after 2 years is approximately $38247$.
- The accumulated value of the second investment after 1.5 years is approximately $46260$.
So, based on accumulated value alone, the second investment yields a higher amount despite the lower interest rate because of the larger monthly deposit.
**Final answer:**
- First investment accumulated value: $38247$
- Second investment accumulated value: $46260$