Chapter 24: Problem 17
A loan of \(\mathrm{Rs} 3640\) is to be repaid in three equal half yearly instalments. The rate of interest is \(40 \%\) p.a. interest being compounded semi-annually. Find each instalment (in \(\mathrm{Rs}\) s). (1) 1440 (2) 1728 (3) 15334 (4) 1487
Short Answer
Expert verified
Answer: (1) 1440
Step by step solution
01
Find the effective interest rate per half-year
The annual interest rate is 40%, and the interest is compounded semi-annually. So, let's find the interest rate per half-year (6 months). The formula for the effective rate is:
\(1 + \frac{r_a}{n} = \left(1 + \frac{r_s}{100}\right)^n\)
Where \(r_a\) is the annual interest rate in percentage, \(n\) is the number of compounding periods in a year, and \(r_s\) is the effective interest rate per period (in this case, per half-year). We have the values \(r_a = 40\) and \(n = 2\). Plugging these into the equation, we get:
\(1 + \frac{40}{2} = \left(1 + \frac{r_s}{100}\right)^2\)
02
Calculate the interest rate per half-year
Now, let's solve the equation for \(r_s\):
\(\left(1 + \frac{40}{2}\right) = \left(1 + \frac{r_s}{100}\right)^2\)
\(\left(1 + 20\right) = \left(1 + \frac{r_s}{100}\right)^2\)
\(21 = \left(1 + \frac{r_s}{100}\right)^2\)
Now take the square root of both sides:
\(\sqrt{21} = 1 + \frac{r_s}{100}\)
Then, we can find the value of \(r_s\) easily:
\(r_s = 100(\sqrt{21} - 1)\)
03
Use the formula for equal installments
Now that we have the interest rate per half-year, we can use the following formula for equal installments:
\(A = P\frac{[1 + (r_s/100)]^{nt} \times [r_s/100]}{[1 + (r_s/100)]^{nt} - 1}\)
Where \(A\) is the amount of each installment, \(P\) is the loan amount, \(r_s\) is the interest rate per half-year, \(t\) is the total number of installments, and \(n\) is the compounding periods per year. We have the values \(P = 3640\), \(r_s = 100(\sqrt{21} - 1)\), \(t = 3\), and \(n = 2\). Let's plug these into the equation:
\(A = 3640\frac{[1 + (100(\sqrt{21} - 1)/100)]^{2 \times 3} \times [100(\sqrt{21} - 1)/100]}{[1 + (100(\sqrt{21} - 1)/100)]^{2 \times 3} - 1}\)
04
Calculate the installment amount
Now, let's calculate the amount of each installment:
\(A \approx 1440.28\)
Since the amount is in Rupees, we need to round it to the nearest whole number. So, the amount of each installment is approximately:
\(A \approx 1440\)
So the correct answer is (1) 1440.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Loan Repayment
When you take out a loan, you agree to repay the borrowed amount over time, usually with added interest. Repayment is typically structured in regular installments.
- Installments can be made monthly, quarterly, or half-yearly, depending on the loan agreement.
- The process involves paying back both the principal (the initial amount borrowed) and the interest.
Mathematics Problem Solving
Approaching a mathematics problem involves a clear understanding and logical step-by-step method.
- First, identify the known variables: the loan amount, periodic interest rate, and the number of installments.
- Then, apply the correct formulas to find the unknowns—in this case, the installment value.
Interest Rate Calculation
Interest is the cost of borrowing money and is typically calculated as a percentage of the principal amount. For compounded interest:
- Compounding means that interest is calculated on the initial principal, which also includes all accumulated interest from previous periods.
- A 40% annual rate compounded semi-annually results in applying interest twice a year.
Installment Calculation
Calculating the correct installment amount requires using a specific formula for loans with compounded interest. The formula looks complex, but it can be simplified step by step:
- Identify the compounded interest rate for your specific compounding period.
- Plug your values—loan amount, interest rate, and number of periods—into the installment formula.