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) Anthony had to pay $4945 in order to furnish the loan taken 3 years before. If the rate of simple interest was 5% then find the sum borrowed.

(2) Find the amount to be paid if William borrowed a sum of $5500 at 5% simple interest for 7 years.

(3) What amount will be due after 2 years if Michael borrowed a sum of $3150 at a 9% simple interest?

(4) What amount does James have to pay after 5 years if he takes a loan of $3000 at 6% simple interest?

(5) Calculate the amount due after 10 years if Michael borrowed a sum of $5300 at a rate of 7% simple interest.

(6) Find the amount to be paid if David borrowed a sum of $5400 at 7% simple interest for 7 years.

(7) How much loan did Dorothy borrow 5 years ago at a rate of simple interest 3% per annum, if he paid $8337.5 to clear it?

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

(9) Calculate the amount due after 9 years if Robert borrowed a sum of $5100 at a rate of 3% simple interest.

(10) What amount does Richard have to pay after 5 years if he takes a loan of $3600 at 3% simple interest?