Question:
Robert had to pay $3379 in order to furnish the loan taken 3 years before. If the rate of simple interest was 3% then find the sum borrowed.
Correct Answer
$3100
Solution And Explanation
Solution
Given,
Amount (A) = $3379
Rate of Simple Interest (R) = 3%
Time (T) = 3 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
$3379 = P (1 + 3% × 3)
⇒ $3379 = P (1 + 3/100 × 3)
⇒ $3379 = P (1 + 3 × 3/100)
⇒ $3379 = P (1 + 9/100)
⇒ $3379 = P (100 + 9/100)
⇒ $3379 = P × 109/100
⇒ P × 109/100 = $3379
⇒ P = 3379/109/100
⇒ P = 3379 × 100/109
⇒ P = 3379 × 100/109
⇒ P = 337900/109
⇒ P = $3100
Thus, the sum borrowed (P) = $3100 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 = 3 years
So, we need to calculate the simple interest for the given time period, which is 3 years
Thus, Simple Interest for 3 years = 3 × Simple Interest for 1 year
= 3 × 3 = 9
Thus, simple interest for 3 years = 9
Thus, Amount (A) = Principal + Interest
⇒ Amount = 100 + 9 = 109
Calculation of the Principal
Now,
∵ If the Amount is 109, then the Principal = 100
∴ If the Amount is 1, then the Principal = 100/109
∴ If the Amount is 3379, then the Principal = 100/109 × 3379
= 100 × 3379/109
= 337900/109
= 3100
Thus, Principal = $3100
Thus, the sum borrowed = $3100 Answer
Similar Questions
(1) Calculate the amount due after 9 years if Christopher borrowed a sum of $6000 at a rate of 4% simple interest.
(2) Sandra took a loan of $6900 at the rate of 6% simple interest per annum. If he paid an amount of $11040 to clear the loan, then find the time period of the loan.
(3) Michael took a loan of $4600 at the rate of 10% simple interest per annum. If he paid an amount of $8740 to clear the loan, then find the time period of the loan.
(4) What amount does Christopher have to pay after 6 years if he takes a loan of $4000 at 10% simple interest?
(5) Calculate the amount due if Patricia borrowed a sum of $3150 at 3% simple interest for 4 years.
(6) Calculate the amount due if Mary borrowed a sum of $3050 at 5% simple interest for 3 years.
(7) What amount does Mary have to pay after 6 years if he takes a loan of $3050 at 4% simple interest?
(8) What amount does Elizabeth have to pay after 5 years if he takes a loan of $3450 at 5% simple interest?
(9) What amount does Barbara have to pay after 5 years if he takes a loan of $3550 at 3% simple interest?
(10) What amount does Susan have to pay after 6 years if he takes a loan of $3650 at 3% simple interest?