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APPLICATION A credit card account is essentially a loan. A constant percent interest is added to the balance. Stanley buys \(\$ 100\) worth of groceries with his credit card. The balance then grows by \(1.75 \%\) interest each month. How much will he owe if he makes no payments in 4 months? Write the expression you used to do this calculation in expanded form and also in exponential form. (a)

Short Answer

Expert verified
Stanley will owe approximately $107.18 after 4 months.

Step by step solution

01

Understanding the Initial Conditions

Stanley has an initial debt of $100 on his credit card. This amount will grow by a constant monthly interest rate of 1.75% if no payments are made. Our task is to find the balance after 4 months with compounding interest.
02

Convert the Interest Rate to Decimal Form

The monthly interest rate provided is 1.75%. To use this in calculations, convert it to decimal form by dividing by 100: \( 1.75\% = \frac{1.75}{100} = 0.0175 \).
03

Set Up the Expression in Expanded Form

The expanded form shows the balance compounding month by month. After 1 month, the balance is \( 100 \times (1 + 0.0175) \) .After 4 months, the expression in expanded form is:\[100 \times (1 + 0.0175) \times (1 + 0.0175) \times (1 + 0.0175) \times (1 + 0.0175)\]
04

Simplify to Exponential Form

The expanded form can be represented in exponential form due to repeated multiplication:\[100 \times (1 + 0.0175)^4\]This shows the initial amount compounded over 4 months.
05

Calculate the Final Amount

Now, calculate the amount Stanley owes by evaluating the exponential expression:\[100 \times (1.0175)^4 \approx 100 \times 1.0718 = 107.18\]The final amount Stanley owes is approximately $107.18.

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Key Concepts

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

Exponential Growth
Exponential growth often appears in the context of compound interest, where an amount increases by a certain percentage over regular intervals. In Stanley's case, his credit card balance grows exponentially because it is increased by the same percentage each month. Each time the balance grows, it does so not just on the initial amount, but also on the previous month's increase.

This can be visualized with the mathematical expression for exponential growth: \[ A = P(1 + r)^t \]where:
  • A is the amount of money accumulated after a certain number of intervals (months in this case).
  • P is the principal amount or the initial amount of money (in this scenario, $100).
  • r is the rate of interest (0.0175 here).
  • t is the time the money is invested or borrowed for in months (4 months for Stanley).
This formula shows how the balance compounds over multiple periods, thus demonstrating exponential growth.
Financial Arithmetic
Financial arithmetic involves calculating various financial scenarios using mathematical operations. In the case of Stanley and his credit card debt, it's about understanding how his balance increases over time due to interest.

To better understand this, consider how each month's interest is calculated. For Stanley:
  • During the first month, the interest is calculated on the initial $100, growing the balance to \(100 \times (1 + 0.0175)\).
  • In the second month, the interest calculation uses the new balance from the first month, continuing as \((100 \times (1.0175)) \times (1.0175)\).
This pattern repeats for each subsequent month. Financial arithmetic relies heavily on these iterative calculations to predict outcomes over time, ensuring one understands how values change due to interest rates and time lapses.
Interest Calculation
Interest calculation is a fundamental part of financial transactions, notably in loans and savings. When using compound interest, as Stanley's case illustrates, it involves calculating interest on both the initial principal and accrued interest from previous periods.

For simple calculations, convert the percentage rate to a decimal; Stanley's rate of 1.75% becomes 0.0175. Then, use this decimal in formulas to evaluate the compounded amount:

Stanley's debt calculation derived from:
  • Expanded Form: Reflects every individual increment: \(100 \times (1 + 0.0175) \times (1 + 0.0175) \times (1 + 0.0175) \times (1 + 0.0175)\).
  • Exponential Form: Summarizes these increments succinctly: \(100 \times (1.0175)^4\).
  • Final calculation leads to an approximate debt of $107.18 after four months.
Understanding interest calculations helps in making informed financial decisions, distinguishing between simple and compound interest scenarios, and planning effectively for future financial standings.

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