Question 1

A sum of money is invested at 10% per annum. The difference between compound interest and simple interest for 2 years is ₹40. Find the principal amount.

Accepted Answer

Step 1: Use the formula for difference between CI and SI for 2 years: Difference = P × (R/100)²

Step 2: Substitute the known values: 40 = P × (10/100)²

Step 3: Simplify: 40 = P × (1/10)² = P × (1/100) = P/100

Step 4: Solve for P: P = 40 × 100 = ₹4,000

Verification:
SI for 2 years = (4000 × 10 × 2)/100 = ₹800
CI for 2 years = 4000(1.10)² - 4000 = 4000(1.21) - 4000 = 4840 - 4000 = ₹840
Difference = 840 - 800 = ₹40 ✓

Therefore, the principal is ₹4,000.

Question 2

A sum of money becomes ₹4,800 after 4 years at a simple interest rate of 5% per annum. What is the principal amount?

Accepted Answer

Step 1: Use the formula A = P + SI, where SI = (P × R × T) / 100. Step 2: We have 4800 = P + (P × 5 × 4) / 100. Step 3: 4800 = P + 0.2P = 1.2P. Step 4: P = 4800 / 1.2 = ₹4,000.

RRB Group D Simple & Compound Interest Questions

RRB Group D Simple & Compound Interest — Past Exam Questions

Study by Subtopic — Simple & Compound Interest

Study Next — Quantitative Aptitude Topics