Formulas for Simple Interest Problems

Formulas based Questions on Simple Interest

Example 1.  Find the simple interest on Rs. 65,000 at 6(2/3)% per annum for a period of 9 months?

Options
(A) 3520
(B) 3250
(C) 2350
(D) 5320

Solution      Principle = 65,000

Rate = 6 \frac{2}{3} \

Time = 9 months

Principle = 65,000

Rate =  \frac{20}{3} \

Time = \frac{3}{4} \

S.I =  \frac{P*R*T}{100} \

= Rs. [65000×(20/3)×(3/4)×(1/100)]

= 3250

Correct Option(B)

Example 2. What sum of money will amount to Rs. 520 in 5 years and Rs. 568 in 7 years at simple interest?

Options
(A) 350
(B) 400
(C) 550
(D) 500

Solution     Amount in 5 years = Rs 520

Amount in 7 years = Rs 568

2 years  S.I = 568-520 = 48

Simple Interest for 1 years = \frac{48}{2} \ = 24

5 years amount = Rs 520

For 1 years = 5*24 = 120

P = A – S.I = 520-120

P = 400

                    Correct Option(B)

Example 3 : At what rate, percent per annum will a sum of money triple in 13 years approximately.

                    Options
                    (A) 2.25%
                    (B) 8.98%
                    (C) 15.38%
                    (D) None

Solution : Let principal = P, Then, S.I.= 2P and Time = 13 years
                  We know that S.I. = \frac{PTR}{100}
                  Rate = \frac{100*2P}{P*13}% = 15.38% per annum.

                 Correct option : 15.38% 

Example 4 : A sum was put at simple interest at a certain rate for 9 years. Had it been put at a 5% higher rate, it would have fetched Rs 540 more. Find the sum.

                   Options
                   (A) 5278 rs
                   (B) 1200 rs
                   (C) 627 rs
                   (D) 3200 rs
                 
Solution:   Let sum = P and original rate = R. Then

                   [\frac{(P \times (R+5) \times 9)}{100}] – [\frac{(P \times R \times 9)}{100}] = 540
                    9P \times (R+5) – 9PR = 54000
                   9PR + 45P – 9PR = 54000
                   45P = 54000
                   P = 1200

                    Correct Option : 3200 Rs

Example 5 : A sum of money at simple interest amounts to Rs. 873 in 6 years and to Rs. 923 in 9 years. The sum is:

                    Options 
                    (A) 624 rs
                    (B) 573 rs
                    (C) 362 rs
                    (D) none

Solution:  S.I. for 1 year =  Rs. (923 – 873) = Rs. 50.

                  S.I. for 6 years = Rs.(50 * 6) = Rs. 300.

                  Principal = Rs. (873 – 300) = Rs. 573

                 Correct Option: 573 Rs