
How to Solve Compound Interest Problems for NID 2025 : Compound interest is an important concept for NID exam preparation as it tests your mathematical proficiency, logical thinking, and ability to apply formulas under time constraints. To solve compound interest problems for NID 2025, candidates must first understand the fundamental formula and the key variables involved. Practice questions to learn the application of formula for different compounding intervals when necessary. Regular practice will help in mastering both basic and complex compound interest problems.
Alternatively, we can write the formula as given below:
- A = amount
- P = principal
- r = rate of interest
- n = number of times interest is compounded per year
- t = time (in years)
CI = A – PThis formula is also called the periodic compounding formula.
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1. Basic Compound Interest Calculation
These problems ask you to calculate the total amount after interest is applied over a specified time period, using the standard compound interest formula. Example : Calculate the amount of money after 3 years if ₹5,000 is invested at an annual interest rate of 6%, compounded annually.2. Finding the Compound Interest
In this type, you are asked to find only the interest earned, rather than the total amount. You will need to subtract the principal from the total amount after compounding. Example: If ₹10,000 is invested at 5% annually for 4 years, calculate the compound interest earned.3. Compound Interest with Different Compounding Frequencies
Problems that involve different compounding frequencies like quarterly, monthly, or daily. You need to adjust the formula accordingly by changing the compounding periods. Example: Calculate the amount if ₹7,000 is invested at an annual interest rate of 8%, compounded monthly for 2 years.4. Half-Yearly and Quarterly Compounding
These are specific cases where interest is compounded semi-annually (twice a year) or quarterly (four times a year). You must adjust the formula for the number of compounding periods in a year. Example : ₹15,000 is invested for 3 years at 6% interest, compounded quarterly. Calculate the total amount at the end of the term.5. Time-Based Compound Interest Problems
These problems ask for the time required to achieve a certain amount of growth or interest. You’ll need to rearrange the compound interest formula to solve for time. Example: How long will it take for ₹8,000 to grow to ₹10,000 at 7% compound interest, compounded annually?6. Comparing Different Investment Options
These problems involve comparing different investments or scenarios where principal, rate of interest, and time periods may differ. You are asked to calculate and compare the total amounts or interest earned in various situations. Example: Compare the compound interest earned on ₹5,000 at 6% for 2 years, compounded quarterly, versus ₹5,000 at 6% for 2 years, compounded annually. Read More: NID Exam Pattern 2025 (Prelims & Mains), Marking Scheme, Weightage Distribution Structure1. If P = 20,000, Rate of Interest = 3% p.a. Time = 2 years three months, Find Compound interest.
Solution:
3% of 20000, i.e. Rs. 600 Rs. 600 will be the interest every year 3% of 600 for 2nd-year compound interest, is 18 So, the 2nd year interest is 600 + 18 = 618 For the 3rd year, 3% interest on 600 of the 1st year and 600 of the 2nd year, i.e. 3% of 1200, i.e. 36. And 3% interest of 18, i.e. 0.54. So, we will take interest of 2 years total and 1/4th interest of 3rd year Compound interest (CI) = 600 (1st year) + 618 (2nd year) + 159.135 (3 months) = 1377.135Compound Interest (CI) = 1377.135
2 . ₹5,000 is invested at an annual interest rate of 6%, compounded annually for 3 years. What will be the total amount at the end of the period?
Solution:
Principal P=5000P Rate r=6%=0.06 Compounded annually ( n=1 ) Time t=3 years A=5000(1+0.06/1)^(1×3) =5000(1+0.06)^3 =5000×(1.06)^3Total Amount (A) = INR 5955.08 .
3. If the difference between Compound interest and simple interest on a certain sum of money at 5% p.a. for three years is Rs. 122. Find the sum.
Solution: For 3 years, the difference between CI and SI is given by the formula: Difference = P * (R/100)^2 * (300 + R) / 100 Substituting the given values: 122 = P * (5/100)^2 * (305/100) Simplifying: 122 = P * (25/10000) * (305/100) Solving for P: P = (122 * 10000 * 100) / (25 * 305) P = 16000 Therefore, the sum is Rs. 16000.4. Find the compound interest (CI) on Rs. 10,000 for 2 years at 15% per annum compounded annually.
Solution:
Principal (P) = Rs. 10,000 Rate (R) = 15 Number of years (n) = 2 A = P[1 +(R/100)]n = 10000[1 + (15/100)]2 = 1000[(100 + 15)/100)]2 = 10000 [(115)/100]2 = 10000 × 1.152 = 10000 × 1.3225 = 13225 Total amount, A = Rs. 13,225 Compound interest (CI) = A – P = Rs. 13,225 – Rs. 10,000Compound interest (CI) = Rs. 3,225
5. Find the compound interest (CI) on Rs. 10,000 for 2 years at 25% per annum compounded annually.
Solution:
Principal (P) = Rs. 10,000 Rate (R) = 15 Number of years (n) = 2 A = P[1 +(R/100)]n = 10000[1 + (25/100)]2 = 1000[(100 + 25)/100)]2 = 10000 [(125)/100]2 = 10000 × 1.252 = 10000 × 1.5625 = 15625 Total amount, A = Rs. 15,625 Compound interest (CI) = A – P = Rs. 15,625 – Rs. 10,000Compound interest (CI) = Rs. 5,625
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