Lela invests $120,000 in a bank. The interest rate is 4.65% per annum, compounded monthly. a) Write a recurrence relation to model Lela's investment. (Note that the question refers to Mikayla, but should be Lela). b) Determine the amount of money in Lela's account after 2 years.

Applied MathematicsCompound InterestRecurrence RelationFinancial MathematicsExponential Growth
2025/3/18

1. Problem Description

Lela invests $120,000 in a bank. The interest rate is 4.65% per annum, compounded monthly.
a) Write a recurrence relation to model Lela's investment. (Note that the question refers to Mikayla, but should be Lela).
b) Determine the amount of money in Lela's account after 2 years.

2. Solution Steps

a) Recurrence relation:
Let AnA_n be the amount in the account after nn months.
The initial amount is A0=120000A_0 = 120000.
The annual interest rate is 4.65%, so the monthly interest rate is 4.65%12=0.046512=0.003875\frac{4.65\%}{12} = \frac{0.0465}{12} = 0.003875.
Each month, the amount in the account is multiplied by 1+0.003875=1.0038751 + 0.003875 = 1.003875.
Therefore, the recurrence relation is:
An+1=An×(1+0.046512)=An×1.003875A_{n+1} = A_n \times (1 + \frac{0.0465}{12}) = A_n \times 1.003875
A0=120000A_0 = 120000
b) Amount after 2 years:
Since the interest is compounded monthly, we need to find the amount after 2×12=242 \times 12 = 24 months.
The formula for compound interest is:
A=P(1+r/n)ntA = P(1 + r/n)^{nt}
where:
AA = the future value of the investment/loan, including interest
PP = the principal investment amount ($120000)
rr = the annual interest rate (decimal) ($0.0465)
nn = the number of times that interest is compounded per year ($12)
tt = the number of years the money is invested or borrowed for ($2)
A=120000(1+0.046512)12×2A = 120000(1 + \frac{0.0465}{12})^{12 \times 2}
A=120000(1+0.003875)24A = 120000(1 + 0.003875)^{24}
A=120000(1.003875)24A = 120000(1.003875)^{24}
A=120000×1.096353A = 120000 \times 1.096353
A=131562.36A = 131562.36

3. Final Answer

a) The recurrence relation is:
An+1=1.003875AnA_{n+1} = 1.003875 A_n
A0=120000A_0 = 120000
b) The amount of money in Lela's account after 2 years is approximately $131562.36.

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