Math Problem Statement

Omar wants to open an account for his grandchildren that he hopes will have $80,000 in it after 20 years. How much must he deposit now into an account that yields 1.75% interest, compounded monthly, so he can be assured of reaching his goal?

Solution

This is a compound interest problem. To calculate how much Omar must deposit now, we can use the formula for compound interest:

A=P(1+rn)ntA = P \left(1 + \frac{r}{n}\right)^{nt}

Where:

  • AA is the amount of money in the future (in this case, $80,000).
  • PP is the present value or the initial deposit (what we need to find).
  • rr is the annual interest rate (1.75% or 0.0175).
  • nn is the number of times the interest is compounded per year (monthly compounding means n=12n = 12).
  • tt is the time the money is invested for (20 years).

We need to solve for PP, the initial deposit:

P=A(1+rn)ntP = \frac{A}{\left(1 + \frac{r}{n}\right)^{nt}}

Substituting the values:

P=80,000(1+0.017512)12×20P = \frac{80,000}{\left(1 + \frac{0.0175}{12}\right)^{12 \times 20}}

Let me calculate this for you.Omar must deposit approximately $56,389.42 now to ensure that the account grows to $80,000 in 20 years with an interest rate of 1.75% compounded monthly.

Would you like more details on this or have any questions?

Here are 5 related questions you might find interesting:

  1. What if the interest was compounded quarterly instead of monthly?
  2. How would the result change if the interest rate was 2% instead of 1.75%?
  3. How much interest would accumulate over the 20 years?
  4. How would the required deposit change if Omar wanted to reach $100,000 instead of $80,000?
  5. What if Omar planned to make annual deposits instead of a lump-sum?

Tip: In compound interest problems, the more frequently the interest is compounded, the higher the final amount will be for the same initial deposit.

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Math Problem Analysis

Mathematical Concepts

Compound Interest
Exponential Growth

Formulas

A = P(1 + r/n)^(nt)
P = A / (1 + r/n)^(nt)

Theorems

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Suitable Grade Level

Grades 11-12