Simple Interest
Math MCQs

Question :    Calculate the amount due if Robert borrowed a sum of $3100 at 9% simple interest for 4 years.

Correct Answer  $4216

Solution & Explanation

Solution

Given,

Principal (P) = $3100

Rate of Simple Interest (SI) = 9%

Time (t) = 4 years

Thus, Amount (A) = ?

The Rate of Interest is always calculated per annum, i.e. per year.

Thus, here 9% simple interest means, Rate of Simple Interest (SI) is 9% per annum.

Method (1) Using Formula

Calculation of Simple Interest

Formula to Calculate Simple Interest

Simple Interest (SI) = Principal × Rate × Time

Thus, Simple Interest (SI) = $3100 × 9% × 4

= $3100 ×⁹/₁₀₀ × 4

= ^{3100 × 9 × 4}/₁₀₀

= ^{27900 × 4}/₁₀₀

= ¹¹¹⁶⁰⁰/₁₀₀

= $1116

Thus, Simple Interest = $1116

Calculation of Amount

The total money paid to the lender by a borrower is called the Amount.

In other words, sum of priciple and interest is called the Amount.

Formula to Calculate the Amount

Amount = Principal + Interest

Thus, Amount = $3100 + $1116

= $4216

Thus, Amount to be paid = $4216 Answer

Method (2)

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

Calculation of Amount directly using Principal, SI, and Time

Formula to calculate the Amount

Amount (A) = Principal (P) + Principal(P) × Rate of Interest (SI) × Time (t)

⇒ A = P + PRT

Here in the question, P = $3100

Rate of Simple Interest (SI) or (R) = 9%

And, Time (t) = 4 years

Thus, Amount (A)

= $3100 + ($3100 × 9% × 4)

= $3100 + ($3100 ×⁹/₁₀₀ × 4)

= $3100 + (^{3100 × 9 × 4}/₁₀₀)

= $3100 + (^{27900 × 4}/₁₀₀)

= $3100 + (¹¹¹⁶⁰⁰/₁₀₀)

= $3100 + $1116 = $4216

Thus, Amount (A) to be paid = $4216 Answer

Method (3) Unitary Method

Calculation of Amount using Unitary Method

Calculation of Interest using Unitary Method

Here, given Rate of Simple Interest = 9%

This, means, $9 per $100 per year

∵ For $100, the simple interest for 1 year = $9

∴ For $1, the simple interest for 1 year = ⁹/₁₀₀

∴ For $3100, the simple interest in 1 year

= ⁹/₁₀₀ × 3100

= ^{9 × 3100}/₁₀₀

= ²⁷⁹⁰⁰/₁₀₀ = $279

Thus, simple interest for 1 year = $279

Therefore, simple interest for 4 years

= Simple interest for 1 year × 4

= $279 × 4 = $1116

Thus, Simple Interest (SI) = $1116

Calculation of Amount

Amount = Principal + Interest

Thus, Amount = $3100 + $1116

= $4216

Thus, Amount to be paid = $4216 Answer

Similar Questions

(1) Robert took a loan of $4200 at the rate of 7% simple interest per annum. If he paid an amount of $6552 to clear the loan, then find the time period of the loan.

(2) Calculate the amount due after 9 years if Richard borrowed a sum of $5600 at a rate of 8% simple interest.

(3) Mary took a loan of $4100 at the rate of 9% simple interest per annum. If he paid an amount of $7421 to clear the loan, then find the time period of the loan.

(4) Calculate the amount due if Joseph borrowed a sum of $3700 at 4% simple interest for 4 years.

(5) What amount does Elizabeth have to pay after 5 years if he takes a loan of $3450 at 2% simple interest?

(6) In how much time a principal of $3150 will amount to $3433.5 at a simple interest of 3% per annum?

(7) Find the amount to be paid if Barbara borrowed a sum of $5550 at 7% simple interest for 7 years.

(8) Calculate the amount due after 9 years if Robert borrowed a sum of $5100 at a rate of 5% simple interest.

(9) In how much time a principal of $3000 will amount to $3450 at a simple interest of 3% per annum?

(10) If Thomas paid $4104 to settle his loan which he had taken 4 years before at a simple interest of 2%, then find the loan taken.