SBI PO Mains Compound Interest Questions are more advanced than the direct formula-based questions generally seen in Prelims. Mains-level CI problems often combine successive interest rates, half-yearly or quarterly compounding, installments, depreciation, CI-SI differences, multi-year rate changes, and Data Interpretation caselets. Candidates should focus on shortcut methods and multi-step calculations to improve accuracy and speed. Free PDFs, quizzes, and high-level arithmetic practice sets can further help in preparing for the Mains exam.
Compound Interest Questions for SBI PO Mains Quiz: 10 Mains-Level Practice Questions
Test your concepts with these exam-oriented compound interest questions for sbi po mains. Attempt each question within 2 minutes before reviewing the solution.
Q1. A sum of ₹X is invested in Scheme A at 12% simple interest for 3 years. The interest earned is then invested in Scheme B at 20% compound interest for 2 years. If the interest from Scheme B is ₹3,168, find X.
Explanation: Scheme A interest = 0.36X. Two-year CI at 20% = 44%, so 0.44×0.36X=3168. Hence X=₹20,000.
Q2. The difference between CI and SI on a sum at 10% p.a. for 3 years is ₹620. Find the difference between CI and SI on the same principal at 20% p.a. for 2 years.
Explanation: For 3 years, CI−SI=P×0.031, so P=₹20,000. For 2 years at 20%, CI−SI=P×0.04=₹800.
Q3. Quantity I: ₹P becomes ₹1.44P in 2 years under CI. Find the interest on ₹(P+5,000) for 2 years at the same rate. Quantity II: SI on ₹30,000 at 15% for 2.5 years.
Explanation: The CI rate is 20%, so Quantity I=44% of (P+5000)=0.44P+2200. Quantity II=₹11,250. Since P is unknown, the relation cannot be established.
Q4. A sum earns CI at 20% p.a. compounded annually for 1.5 years. If half-yearly compounding would give ₹2,410 more interest, find the principal.
Explanation: Annual 1.5-year growth = 1.20×1.10 = 1.32. Half-yearly growth = 1.10³ = 1.331. Difference = 1.1% of principal = ₹2,410. Principal ≈ ₹2,19,090.91.
Q5. A man borrows ₹21,000 at 10% p.a. CI and repays in two equal annual installments. Find each installment.
Explanation: 21000=X/1.1+X/1.1². Solving gives X=₹12,100.
Q6. A sum invested at CI yields ₹2,420 interest in the second year and ₹2,662 in the third year. Find the annual rate.
Explanation: Increase=2662−2420=242. Rate=242/2420×100=10%.
Q7. A machine depreciates by 15% in Year 1 and 20% in Year 2. If its value after 2 years is ₹68,000, find the original value.
Explanation: Final value=P×0.85×0.80=0.68P. Thus P=₹1,00,000.
Q8. Sumit borrows ₹15,000 at 10% CI. At the end of each of the first two years, he pays ₹3,000. How much should he pay at the end of Year 3 to clear the debt?
Explanation: After Year 1 payment, balance=₹13,500. After Year 2 payment, balance=₹11,850. At end of Year 3: 11850×1.10=₹13,035.
Q9. Data Sufficiency: Find the principal under CI. I. CI in 2 years at 10% is ₹2,100. II. CI−SI for 2 years at 10% is ₹100.
Explanation: I: 21% of P=2100 ⇒ P=₹10,000. II: 1% of P=100 ⇒ P=₹10,000. Either alone is sufficient.
Q10. A city's population rises by 20%, falls by 10%, then rises by 25%. If the final population is 1,35,000, find the initial population.
Explanation: Final=P×1.20×0.90×1.25=1.35P. Therefore P=1,00,000.
Quiz Summary
Quiz Completed!
Practise more Simple and Compound Interest questions.
Solve More QuestionsHigh-Level CI Concepts & Shortcuts for SBI PO Mains
To attempt sbi po mains compound interest tricks and shortcuts successfully, move away from long multiplication chains and rely on these structured calculation methods:
1. Effective Percentage Rate Method
Instead of calculating $A = P \left(1 + \frac{R}{100}\right)^n$, convert interest rates into effective percentages using $a + b + \frac{ab}{100}$:
- 10% for 2 Years: $10 + 10 + \frac{100}{100} = 21\%$
- 10% for 3 Years: $21 + 10 + \frac{210}{100} = 33.1\%$
- 20% for 2 Years: $20 + 20 + \frac{400}{100} = 44\%$
2. Multi-Year CI-SI Difference Formulas
- 2-Year Difference: $CI – SI = P \left(\frac{R}{100}\right)^2$
- 3-Year Difference: $CI – SI = P \left(\frac{R}{100}\right)^2 \left(\frac{300 + R}{100}\right)$
3. Compounding Frequency Modifications
When compounding frequency changes, adjust the rate and time variables before applying any formula:
- Half-Yearly: Rate becomes $\frac{R}{2}\%$, Time periods become $2T$.
- Quarterly: Rate becomes $\frac{R}{4}\%$, Time periods become $4T$.
Master CI Data Interpretation Caselets in SBI PO Mains
Missing Data Interpretation (DI) sets based on Simple and Compound Interest frequently appear in Mains. Follow this step-by-step strategy to handle them:
1. Express missing principal or rate via variables (X, Y)
2. Convert yearly interest rates into fraction ratios
3. Formulate equations combining CI and SI schemes
4. Solve using effective percentage or ratio elimination
- Set Up an LCM Baseline: If principal values are missing across multiple schemes, assume an LCM-based baseline (e.g., Rs. 100 or LCM of given rates) to quickly calculate relative interest.
- Isolate Annual Interest Differences: Remember that for any year $N$, the extra interest gained in year $N+1$ under CI is purely the interest calculated on year $N$’s accumulated interest.
Benefits of Practicing Mains Compound Interest Sets
- High Mark Weightage: CI concepts form the core of standalone word problems, Data Sufficiency, Quantity Comparisons ($Q1 \text{ vs } Q2$), and Arithmetic DI caselets.
- Conceptual Overlap: Learning effective percentage growth directly aids in solving population growth, machine depreciation, and profit-and-loss partnership problems.
- Higher Accuracy: Deterministic mathematical rules mean that once an algebraic setup is solved, accuracy approaches $100\%$.
Conclusion
Mastering compound interest questions for SBI PO Mains requires strong conceptual clarity, proficiency in shortcut techniques, and consistent practice with multi-variable caselets. Focus on mastering effective percentage conversions, installment setups, and CI-SI difference relations to maximize your Quantitative Aptitude score.
Frequently Asked Questions (FAQs)
1. What type of Compound Interest questions appear in SBI PO Mains?
SBI PO Mains tests high-level patterns including variable-based CI equations, CI-SI multi-year differences, installment calculations, partial annual repayments, missing DI caselets, and quarterly/half-yearly compounding shifts.
2. How is Mains Compound Interest different from Prelims?
Prelims questions evaluate direct formula application and speed. Mains questions integrate CI into logical caselets, requiring candidates to derive missing variables, handle fractional time periods, or compare two quantities.
3. What is the quickest way to calculate 3-year compound interest?
Use the Ratio Method ($3 : 3 : 1$) or Effective Percentage Rate ($33.1\%$ for $10\%$, $72.8\%$ for $20\%$) instead of expanding $(1 + R/100)^3$.
4. How do you solve loan installment questions in Compound Interest?
Use the present value installment formula: $\text{Loan} = \frac{X}{1 + R/100} + \frac{X}{(1 + R/100)^2} + \dots + \frac{X}{(1 + R/100)^n}$, where $X$ is the equal annual installment amount.
5. Which mock platforms are best for SBI PO Mains Quantitative Aptitude?
Platforms like Testbook, PracticeMock, and Guidely provide exam-oriented PYQs and realistic Mains-level practice sets.
- Sign Up on Practicemock for Updated Current Affairs, Topic Tests and Mini Mocks
- Sign Up Here to Download Free Study Material
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