Simple Interest
Math MCQs

Question :    How much loan did Joseph borrow 5 years ago at a rate of simple interest 3% per annum, if he paid $6555 to clear it?

Correct Answer  $5700

Solution & Explanation

Solution

Given,

Amount (A) = $6555

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

$6555 = P (1 + 3% × 5)

⇒ $6555 = P (1 + ³/₁₀₀ × 5)

⇒ $6555 = P (1 + ^{3 × 5}/₁₀₀)

⇒ $6555 = P (1 + ¹⁵/₁₀₀)

⇒ $6555 = P (^{100 + 15}/₁₀₀)

⇒ $6555 = P × ¹¹⁵/₁₀₀

⇒ P × ¹¹⁵/₁₀₀ = $6555

⇒ P = ⁶⁵⁵⁵/_¹¹⁵/100

⇒ P = 6555 × ¹⁰⁰/₁₁₅

⇒ P = ^{6555 × 100}/₁₁₅

⇒ P = ⁶⁵⁵⁵⁰⁰/₁₁₅

⇒ P = $5700

Thus, the sum borrowed (P) = $5700 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 6555, then the Principal = ¹⁰⁰/₁₁₅ × 6555

= ^{100 × 6555}/₁₁₅

= ⁶⁵⁵⁵⁰⁰/₁₁₅

= 5700

Thus, Principal = $5700

Thus, the sum borrowed = $5700 Answer

Similar Questions

(1) What amount does Mary have to pay after 5 years if he takes a loan of $3050 at 6% simple interest?

(2) Find the amount to be paid if Thomas borrowed a sum of $5800 at 5% simple interest for 8 years.

(3) If Sandra paid $5340 to settle his loan which he had taken 4 years before at a simple interest of 5%, then find the loan taken.

(4) Find the amount to be paid if Sarah borrowed a sum of $5850 at 6% simple interest for 8 years.

(5) What amount will be due after 2 years if William borrowed a sum of $3250 at a 9% simple interest?

(6) William took a loan of $5000 at the rate of 7% simple interest per annum. If he paid an amount of $7450 to clear the loan, then find the time period of the loan.

(7) Calculate the amount due after 10 years if William borrowed a sum of $5500 at a rate of 7% simple interest.

(8) Margaret took a loan of $6700 at the rate of 9% simple interest per annum. If he paid an amount of $12730 to clear the loan, then find the time period of the loan.

(9) Calculate the amount due if David borrowed a sum of $3400 at 2% simple interest for 4 years.

(10) Calculate the amount due after 9 years if David borrowed a sum of $5400 at a rate of 10% simple interest.