Simple Interest
Math MCQs

Question :    How much loan did Kimberly borrow 5 years ago at a rate of simple interest 3% per annum, if he paid $7647.5 to clear it?

Correct Answer  $6650

Solution & Explanation

Solution

Given,

Amount (A) = $7647.5

Rate of Simple Interest (R) = 3%

Time (T) = 5 years

Thus, Principal (P) = ?

Method (1) Using Formula

Calculation of the Principal using forumula when Amount, Time and Rate of Simple Interest are given

Formula to find the Principal (P)

Amount (A) = Principal (P) + Principal (P) × Rate (R) × Time (T)

⇒ Amount (A) = Principal (P) [1 + Rate (R) × Time (T)]

⇒ A = P (1 + RT)

Using the formula to find the Amount (A), the fourth can be calculated if any three of A, P, R, and T are given

In the given question, we need to find the Principal (P)

Therefore, by substituting, Amount, Rate, and Time, in the formula A = P (1 + RT) we get

$7647.5 = P (1 + 3% × 5)

⇒ $7647.5 = P (1 + ³/₁₀₀ × 5)

⇒ $7647.5 = P (1 + ^{3 × 5}/₁₀₀)

⇒ $7647.5 = P (1 + ¹⁵/₁₀₀)

⇒ $7647.5 = P (^{100 + 15}/₁₀₀)

⇒ $7647.5 = P × ¹¹⁵/₁₀₀

⇒ P × ¹¹⁵/₁₀₀ = $7647.5

⇒ P = ^7647.5/_¹¹⁵/100

⇒ P = 7647.5 × ¹⁰⁰/₁₁₅

⇒ P = ^{7647.5 × 100}/₁₁₅

⇒ P = ⁷⁶⁴⁷⁵⁰/₁₁₅

⇒ P = $6650

Thus, the sum borrowed (P) = $6650 Answer

Method (1) Using Unitary Method

Calculation of the Principal using unitary method when Amount, Time and Rate of Simple Interest are given

Calculation of the Simple Interest

Let, the principal = 100

Here, since rate of simple interest = 3% per annum

Thus, Interest = 3% of principal

⇒ Interest = 3% of 100 = 3

Thus, Simple Interest for 1 year = 3

Calculation of the Amount

Since, in the question, time = 5 years

So, we need to calculate the simple interest for the given time period, which is 5 years

Thus, Simple Interest for 5 years = 5 × Simple Interest for 1 year

= 5 × 3 = 15

Thus, simple interest for 5 years = 15

Thus, Amount (A) = Principal + Interest

⇒ Amount = 100 + 15 = 115

Calculation of the Principal

Now,

∵ If the Amount is 115, then the Principal = 100

∴ If the Amount is 1, then the Principal = ¹⁰⁰/₁₁₅

∴ If the Amount is 7647.5, then the Principal = ¹⁰⁰/₁₁₅ × 7647.5

= ^{100 × 7647.5}/₁₁₅

= ⁷⁶⁴⁷⁵⁰/₁₁₅

= 6650

Thus, Principal = $6650

Thus, the sum borrowed = $6650 Answer

Similar Questions

(1) How much loan did Deborah borrow 5 years ago at a rate of simple interest 4% per annum, if he paid $8940 to clear it?

(2) Donald took a loan of $7000 at the rate of 10% simple interest per annum. If he paid an amount of $12600 to clear the loan, then find the time period of the loan.

(3) Find the amount to be paid if John borrowed a sum of $5200 at 2% simple interest for 8 years.

(4) Calculate the amount due if Patricia borrowed a sum of $3150 at 4% simple interest for 3 years.

(5) Susan took a loan of $5300 at the rate of 7% simple interest per annum. If he paid an amount of $8639 to clear the loan, then find the time period of the loan.

(6) Calculate the amount due after 9 years if Christopher borrowed a sum of $6000 at a rate of 2% simple interest.

(7) What amount will be due after 2 years if Michael borrowed a sum of $3150 at a 4% simple interest?

(8) Thomas took a loan of $5600 at the rate of 7% simple interest per annum. If he paid an amount of $8736 to clear the loan, then find the time period of the loan.

(9) Calculate the amount due if Richard borrowed a sum of $3600 at 4% simple interest for 4 years.

(10) Calculate the amount due if James borrowed a sum of $3000 at 10% simple interest for 4 years.