SSC CGL (Prelims) General: Simple Interest and Compound Interest questions with solutions

Q1. A laptop is available for ₹25,800 in cash or for ₹4,200 as a down payment and three equal annual instalments. If the seller charges interest at 12% per annum compounded annually, calculate the amount of each instalment.

1. ₹ 8,993
2. ₹ 9,150
3. ₹ 9,452
4. ₹ 9,720

Answer: ₹ 8,993

The financed amount is ₹25,800 - ₹4,200 = ₹21,600. Let each instalment be ₹x paid at the end of years 1, 2, and 3; its present value is \(\frac{x}{1.12}+\frac{x}{1.12^2}+\frac{x}{1.12^3}\). Equating this to ₹21,600 and solving gives \(x \approx ₹8,993\).

Q2. A person invested certain amounts in three different schemes A, B, and C at simple interest rates of 8% p.a., 10% p.a., and 13% p.a. respectively. If the total interest in one year was ₹3,360 and the amount invested in Scheme C was 300% of the amount in Scheme A and 400% of the amount in Scheme B, what was the amount invested in Scheme A?

1. ₹ 7,127
2. ₹ 7,500
3. ₹ 6,165
4. ₹ 8,500

Answer: ₹ 6,165

Let the amount in Scheme A be \(x\). Then Scheme C = 300% of A = \(3x\), and since C = 400% of B, B = \(\frac{3x}{4}\). Total one-year interest is \(0.08x + 0.10\cdot\frac{3x}{4} + 0.13\cdot 3x = 3360\). Solving gives \(x = 6165\).

Q3. The compound interest on a certain sum for 2 years at 10% per annum is ₹840. Find the simple interest on the same sum at the same rate and for the same period.

1. ₹ 850
2. ₹ 820
3. ₹ 780
4. ₹ 800

Answer: ₹ 800

For 2 years at 10%, compound interest is 21% of the principal. So 0.21P = 840, giving P = 4000. Simple interest for 2 years at 10% is 20% of 4000 = 800.