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Equity in a home: When you purchase a home by securing a mortgage, the total paid toward the principal is your equity in the home. (Technically, the lending agency calculates your equity by subtracting the amount you still owe on your mortgage from the current value of your home, which may be higher or lower than your principal.) If your mortgage is for \(P\) dollars, and if the term of the mortgage is \(t\) months, then your equity \(E\), in dollars, after \(k\) monthly payments is given by $$ E=P \times \frac{(1+r)^{k}-1}{(1+r)^{t}-1} $$ Here \(r\) is the monthly interest rate as a decimal, with \(r=\mathrm{APR} / 12\).c. Find a formula that gives your equity after \(y\) years of payments. Suppose you have a home mortgage of \(\$ 400,000\) for 30 years at an APR of \(6 \%\). a. What is the monthly rate as a decimal? Round your answer to three decimal places. b. Express, using functional notation, your equity after 20 years of payments, and then calculate that value.

Short Answer

Expert verified
The monthly rate is 0.005, and the equity after 20 years is approximately $153,592.

Step by step solution

01

Convert APR to Monthly Rate

To find the monthly rate as a decimal, divide the APR by 12. The APR is given as 6%, so first convert it to a decimal by dividing by 100: \( \text{APR as a decimal} = \frac{6}{100} = 0.06 \). Now divide by 12 to find the monthly rate: \( r = \frac{0.06}{12} = 0.005 \).
02

Define Months in Years

To express the number of payments in years, compute the total months for any given number of years. Since there are 12 months in a year, 20 years equals \( 20 \times 12 = 240 \) months.
03

Define the Equity Formula for 'y' Years

Replace \( k \) with \( 12y \) in the equity formula to get it in terms of years \( y \): \[ E(y) = P \times \frac{(1+r)^{12y}-1}{(1+r)^{t}-1} \] where \( t = 30 \times 12 = 360 \) for a 30-year mortgage.
04

Calculate Equity After 20 Years

Use the formula from Step 3 and substitute the values: \( P = 400,000 \), \( r = 0.005 \), and \( y = 20 \). Compute: \[ E(20) = 400,000 \times \frac{(1+0.005)^{20 \times 12}-1}{(1+0.005)^{360}-1} \]. Evaluate the expression to get \( E(20) \).
05

Perform the Calculation

Calculate \((1+0.005)^{240} = 3.3102\) and \((1+0.005)^{360} = 6.0226\). Thus: \[ E(20) = 400,000 \times \frac{3.3102 - 1}{6.0226 - 1} = 400,000 \times 0.38398 \approx 153,592 \].

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Key Concepts

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

Equity Calculation
Equity calculation is an essential concept when dealing with financial mathematics related to homeownership. Equity refers to the portion of the property that you own outright, without any debt. When you take out a mortgage to purchase a home, initially, the amount you owe is equal to your mortgage amount. However, as you make monthly payments towards the loan, you gradually increase your equity in the home.

To calculate the equity in your home, you subtract the remaining mortgage balance from the current market value of the property. This means that equity can increase due to two factors: paying down the mortgage balance and appreciation of the property's value. The formula to calculate equity after a certain number of payments takes these factors into consideration and allows homeowners to understand how much of the home they truly own at any given time. In the specific formula provided for calculating equity:
  • \( E = P \times \frac{(1+r)^{k}-1}{(1+r)^{t}-1} \)
**\(E\)** stands for equity, **\(P\)** represents the initial principal or loan amount, **\(r\)** is the periodic interest rate, and \(k\) is the number of periods after which you're calculating equity. This formula helps homeowners forecast their financial status over the term of their mortgage.
Mortgage
A mortgage is a loan specifically used to purchase real estate, where the property itself serves as collateral for the loan. When you arrange a mortgage, you're essentially borrowing money to help finance your home or property purchase.

Mortgages typically have a fixed term, such as 15 or 30 years, during which the borrower makes regular monthly payments. These payments consist of both principal (the original loan amount) and interest.

The purpose of the mortgage is to spread out the high cost of purchasing a home over a longer period, making it more accessible to buyers who might not have the full purchase amount readily available.
  • There are various types of mortgages, including fixed-rate and adjustable-rate mortgages.
  • Fixed-rate mortgages have an interest rate that remains the same for the duration of the loan, providing stability in your monthly payments.
  • Adjustable-rate mortgages (ARMs) may have an interest rate that changes periodically based on market conditions, which can result in varying payment amounts.
Understanding the structure and terms of your mortgage is crucial for managing homeownership expenses effectively.
Interest Rate
Interest rate is a key component in financial mathematics, specifically when calculating repayments on loans, including mortgages. It represents the cost of borrowing money, expressed as a percentage of the principal loan amount.

In the context of a mortgage, the interest rate will determine how much extra you pay on top of repaying the principal amount of the loan. It's an important factor influencing the overall amount payable over the loan period.
  • The Annual Percentage Rate (APR) commonly stated by lenders combines the interest rate with loan fees to give borrowers the yearly cost of the loan.

  • To find the monthly interest rate, which is necessary for calculating monthly mortgage payments, divide the APR by 12.
For example, if the APR is 6%, expressed as a decimal it's 0.06. The monthly interest rate would then be \(r = \frac{0.06}{12} = 0.005\). Understanding how interest rates affect loan costs is crucial for budgeting and financial planning.

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Most popular questions from this chapter

Catering a dinner: You are having a dinner catered. You pay a rental fee of \(\$ 150\) for the dining hall, and you pay the caterer \(\$ 10\) for each person who attends the dinner. a. Suppose you just want to break even. i. How much should you charge per ticket if you expect 50 people to attend? ii. Use a formula to express the amount you should charge per ticket as a function of the number of people attending. Be sure to explain the meaning of the letters you choose and the units. iii. You expect 65 people to attend the dinner. Use your answer to part ii to express in functional notation the amount you should charge per ticket, and then calculate that amount. b. Suppose now that you want to make a profit of \(\$ 100\) from the dinner. Use a formula to express the amount you should charge per ticket as a function of the number of people attending. Again, be sure to explain the meaning of the letters you choose and the units.

How much can I borrow? The function in Example \(1.2\) can be rearranged to show the amount of money \(P=P(M, r, t)\), in dollars, that you can afford to borrow at a monthly interest rate of \(r\) (as a decimal) if you are able to make \(t\) monthly payments of \(M\) dollars: $$ P=M \times \frac{1}{r} \times\left(1-\frac{1}{(1+r)^{r}}\right) . $$ Suppose you can afford to pay \(\$ 350\) per month for 4 years. a. How much money can you afford to borrow for the purchase of a car if the prevailing monthly interest rate is \(0.75 \%\) ? (That is \(9 \%\) APR.) Express the answer in functional notation, and then calculate it. b. Suppose your car dealer can arrange a special monthly interest rate of \(0.25 \%\) (or \(3 \%\) APR). How much can you afford to borrow now? c. Even at \(3 \%\) APR you find yourself looking at a car you can't afford, and you consider extending the period during which you are willing to make payments to 5 years. How much can you afford to borrow under these conditions?

Pole vault: The height of the winning pole vault in the early years of the modern Olympic Games can be modeled as a function of time by the formula \(H=0.05 t+3.3\) Here \(t\) is the number of years since 1900 , and \(H\) is the winning height in meters. (One meter is \(39.37\) inches.) a. Calculate \(H(4)\) and explain in practical terms what your answer means. b. By how much did the height of the winning pole vault increase from 1900 to 1904 ? From 1904 to 1908 ?

Flying ball: A ball is tossed upward from a tall building, and its upward velocity \(V\), in feet per second, is a function of the time \(t\), in seconds, since the ball was thrown. The formula is \(V=40-32 t\) if we ignore air resistance. The function \(V\) is positive when the ball is rising and negative when the ball is falling. a. Express using functional notation the velocity 1 second after the ball is thrown, and then calculate that value. Is the ball rising or falling then? b. Find the velocity 2 seconds after the ball is thrown. Is the ball rising or falling then? c. What is happening \(1.25\) seconds after the ball is thrown? d. By how much does the velocity change from 1 to 2 seconds after the ball is thrown? From 2 to 3 seconds? From 3 to 4 seconds? Compare the answers to these three questions and explain in practical terms.

A car that gets 32 miles per gallon: The cost \(C\) of operating a certain car that gets 32 miles per gallon is a function of the price \(g\), in dollars per gallon, of gasoline and the distance \(d\), in miles, that you drive. The formula for \(C=C(g, d)\) is \(C=g d / 32\) dollars. a. Use functional notation to express the cost of operation if gasoline costs 98 cents per gallon and you drive 230 miles. Calculate the cost. b. Calculate \(C(1.03,172)\) and explain the meaning of the number you have calculated.

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