Simple Interest
Math MCQs

Question :    Calculate the amount due if Robert borrowed a sum of $3100 at 9% simple interest for 3 years.

Correct Answer  $3937

Solution & Explanation

Solution

Given,

Principal (P) = $3100

Rate of Simple Interest (SI) = 9%

Time (t) = 3 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% × 3

= $3100 ×⁹/₁₀₀ × 3

= ^{3100 × 9 × 3}/₁₀₀

= ^{27900 × 3}/₁₀₀

= ⁸³⁷⁰⁰/₁₀₀

= $837

Thus, Simple Interest = $837

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 + $837

= $3937

Thus, Amount to be paid = $3937 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) = 3 years

Thus, Amount (A)

= $3100 + ($3100 × 9% × 3)

= $3100 + ($3100 ×⁹/₁₀₀ × 3)

= $3100 + (^{3100 × 9 × 3}/₁₀₀)

= $3100 + (^{27900 × 3}/₁₀₀)

= $3100 + (⁸³⁷⁰⁰/₁₀₀)

= $3100 + $837 = $3937

Thus, Amount (A) to be paid = $3937 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 3 years

= Simple interest for 1 year × 3

= $279 × 3 = $837

Thus, Simple Interest (SI) = $837

Calculation of Amount

Amount = Principal + Interest

Thus, Amount = $3100 + $837

= $3937

Thus, Amount to be paid = $3937 Answer

Similar Questions

(1) Jennifer took a loan of $4500 at the rate of 7% simple interest per annum. If he paid an amount of $7650 to clear the loan, then find the time period of the loan.

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

(3) Calculate the amount due after 9 years if Susan borrowed a sum of $5650 at a rate of 4% simple interest.

(4) How much loan did Anthony borrow 5 years ago at a rate of simple interest 2% per annum, if he paid $6930 to clear it?

(5) Charles took a loan of $5800 at the rate of 10% simple interest per annum. If he paid an amount of $10440 to clear the loan, then find the time period of the loan.

(6) Charles took a loan of $5800 at the rate of 7% simple interest per annum. If he paid an amount of $9454 to clear the loan, then find the time period of the loan.

(7) What amount does Jennifer have to pay after 5 years if he takes a loan of $3250 at 2% simple interest?

(8) How much loan did Rebecca borrow 5 years ago at a rate of simple interest 4% per annum, if he paid $9180 to clear it?

(9) Calculate the amount due if Mary borrowed a sum of $3050 at 9% simple interest for 3 years.

(10) Find the amount to be paid if John borrowed a sum of $5200 at 6% simple interest for 8 years.