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If you deposit money today in an account that pays \(6.5 \%\) annual interest, how long will it take to double your money?

Short Answer

Expert verified
It will take approximately 11.08 years.

Step by step solution

01

Understanding the Formula

To determine how long it takes to double your money at a given interest rate, you can use the Rule of 72. The Rule of 72 is a simplified formula to estimate the number of years required to double the invested money at a fixed annual rate of interest. It states that the number of years needed to double an investment can be found by dividing 72 by the annual interest rate.
02

Applying the Rule of 72

Use the formula from the Rule of 72 to find the number of years: \( t = \frac{72}{r} \), where \( r \) is the annual interest rate. Here, \( r = 6.5\% \).
03

Calculate the Time

Now substitute the interest rate into the formula: \( t = \frac{72}{6.5} \). Calculate the result to find the approximate number of years it will take for the investment to double.
04

Find the Result

Compute the division: \( t = \frac{72}{6.5} \approx 11.08 \). Therefore, it will take approximately 11.08 years for the money to double at an interest rate of 6.5%.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Compound Interest
Understanding compound interest is essential as it plays a significant role in growing investments over time. Unlike simple interest, which is calculated only on the principal amount, compound interest is calculated on the principal amount plus any previously earned interest. This means the interest is calculated on an ever-growing base, which allows the investment to increase more rapidly.

Here’s how it works: if you deposit a sum into an account with compound interest, the interest from each period is added to the principal for the next period. This process continues until the end of the investment duration. The formula for compound interest is:
  • \( A = P \times \left(1 + \frac{r}{n}\right)^{nt} \)
where:
  • \( A \) is the final amount of money after interest,
  • \( P \) is the initial principal balance,
  • \( r \) is the annual interest rate (as a decimal),
  • \( n \) is the number of times that interest is compounded per year,
  • \( t \) is the time the money is invested for in years.
Compound interest can greatly increase the total amount of an investment over time, leading to exponential growth.
Financial Mathematics
Financial mathematics involves using mathematical formulas and concepts to solve real-life financial problems, such as calculating loan payments, investment returns, and understanding financial products. It helps in making informed decisions about savings, investing, and taking loans.

Some essential equations and principles in financial mathematics include:
  • Present Value and Future Value calculations: These help determine how much an investment is worth today or in the future based on a specific interest rate.
  • Annuities and Perpetuities: These financial products calculate a stream of cash flows over time for various securities and investment options.
  • The Interest Rate and its impact: Understanding how different rates effect calculations is crucial for predicting growth or costs.
Financial mathematics is vital for predicting and analyzing the potential issues and benefits of various financial decisions. Proper use of financial mathematics ensures better planning and management of personal or business finances.
Investment Growth
Investment growth is the increase in the value of an asset or portfolio over time. This growth can result from interest earnings, stock price increases, or the reinvestment of dividends. Understanding how investments grow helps individuals make decisions about where and how to invest their money to achieve financial goals.

Here are some factors affecting investment growth:
  • Time: The length of time you stay invested can significantly impact growth due to the power of compound interest.
  • Rate of Return: Higher interest rates or rates of return typically lead to faster growth, as seen clearly in the Rule of 72 for doubling investments.
  • Risk: With higher potential returns often comes higher risk, and finding a balance is key to successful investing.
Investment growth is not always linear and can be influenced by market conditions, economy changes, or investor behavior. Therefore, diversifying investments and understanding basic principles of growth can help manage risks and maximize returns over time.

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Most popular questions from this chapter

You want to buy a house that \(\operatorname{costs} \$ 100,000 .\) You have \(\$ 10,000\) for a down payment, but your credit is such that mortgage companies will not lend you the required \(\$ 90,000\). However, the realtor persuades the seller to take a \(\$ 90,000\) mortgage (called a seller take-back mortgage) at a rate of \(7 \%\), provided the loan is paid off in full in 3 years. You expect to inherit \(\$ 100,000\) in 3 years; but right now all you have is \(\$ 10,000,\) and you can afford to make payments of no more than \(\$ 7,500\) per year given your salary. (The loan would call for monthly payments, but assume end-of-year annual payments to simplify things.) a. If the loan was amortized over 3 years, how large would each annual payment be? Could you afford those payments? b. If the loan was amortized over 30 years, what would each payment be? Could you afford those payments? c. To satisfy the seller, the 30 -year mortgage loan would be written as a balloon note, which means that at the end of the third year, you would have to make the regular payment plus the remaining balance on the loan. What would the loan balance be at the end of Year \(3,\) and what would the balloon payment be?

A rookie quarterback is negotiating his first NFL contract. His opportunity cost is \(10 \%\). He has been offered three possible 4 -year contracts. Payments are guaranteed, and they would be made at the end of each year. Terms of each contract are as follows: $$\begin{array}{lcccc} & 1 & 2 & 3 & 4 \\\& & & & \\\\\text { Contract 1 } & \$ 3,000,000 & \$ 3,000,000 & \$ 3,000,000 & \$ 3,000,000 \\\\\text { Contract 2 } & \$ 2,000,000 & \$ 3,000,000 & \$ 4,000,000 & \$ 5,000,000 \\\\\text { Contract 3 } & \$ 7,000,000 & \$ 1,000,000 & \$ 1,000,000 & \$ 1,000,000 \end{array}$$ As his adviser, which contract would you recommend that he accept?

a. Set up an amortization schedule for a \(\$ 25,000\) loan to be repaid in equal installments at the end of each of the next 3 years. The interest rate is \(10 \%\) compounded annually. b. What percentage of the payment represents interest and what percentage represents principal for each of the 3 years? Why do these percentages change over time?

Your father is 50 years old and will retire in 10 years. He expects to live for 25 years after he retires, until he is \(85 .\) He wants a fixed retirement income that has the same purchasing power at the time he retires as \(\$ 40,000\) has today. (The real value of his retirement income will decline annually after he retires.) His retirement income will begin the day he retires, 10 years from today, at which time he will receive 24 additional annual payments. Annual inflation is expected to be \(5 \%\). He currently has \(\$ 100,000\) saved, and he expects to earn \(8 \%\) annually on his savings. How much must he save during each of the next 10 years (end-of-year deposits) to meet his retirement goal?

Find the amount to which \(\$ 500\) will grow under each of these conditions: a. \(12 \%\) compounded annually for 5 years b. \(12 \%\) compounded semiannually for 5 years c. \(12 \%\) compounded quarterly for 5 years d. \(12 \%\) compounded monthly for 5 years e. \(12 \%\) compounded daily for 5 years f. Why does the observed pattern of FVs occur?

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