Question:
How much loan did Christopher borrow 5 years ago at a rate of simple interest 3% per annum, if he paid $6900 to clear it?
Correct Answer
$6000
Solution And Explanation
Solution
Given,
Amount (A) = $6900
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
$6900 = P (1 + 3% × 5)
⇒ $6900 = P (1 + 3/100 × 5)
⇒ $6900 = P (1 + 3 × 5/100)
⇒ $6900 = P (1 + 15/100)
⇒ $6900 = P (100 + 15/100)
⇒ $6900 = P × 115/100
⇒ P × 115/100 = $6900
⇒ P = 6900/115/100
⇒ P = 6900 × 100/115
⇒ P = 6900 × 100/115
⇒ P = 690000/115
⇒ P = $6000
Thus, the sum borrowed (P) = $6000 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 6900, then the Principal = 100/115 × 6900
= 100 × 6900/115
= 690000/115
= 6000
Thus, Principal = $6000
Thus, the sum borrowed = $6000 Answer
Similar Questions
(1) Calculate the amount due if Linda borrowed a sum of $3350 at 8% simple interest for 4 years.
(2) Calculate the amount due after 9 years if James borrowed a sum of $5000 at a rate of 6% simple interest.
(3) Calculate the amount due if Sarah borrowed a sum of $3850 at 8% simple interest for 4 years.
(4) If Sandra paid $5162 to settle his loan which he had taken 4 years before at a simple interest of 4%, then find the loan taken.
(5) Calculate the amount due after 9 years if Mary borrowed a sum of $5050 at a rate of 3% simple interest.
(6) What amount does Barbara have to pay after 6 years if he takes a loan of $3550 at 7% simple interest?
(7) What amount does Thomas have to pay after 6 years if he takes a loan of $3800 at 5% simple interest?
(8) Calculate the amount due after 9 years if Thomas borrowed a sum of $5800 at a rate of 10% simple interest.
(9) What amount does Linda have to pay after 5 years if he takes a loan of $3350 at 2% simple interest?
(10) Mary took a loan of $4100 at the rate of 8% simple interest per annum. If he paid an amount of $7380 to clear the loan, then find the time period of the loan.