Simple Interest
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Solved Examples
Study MaterialSolved Examples – Simple Interest
Solved examples help students understand the practical application of Simple Interest concepts in competitive examinations. These examples are designed from basic to advanced level and cover important questions frequently asked in SSC, Banking, Railway, CDS, NDA, UPSC, CAT, Defence, and placement aptitude tests.
Topics Covered in Solved Examples
- Basic Simple Interest Problems
- Amount Calculation
- Principal Finding Problems
- Rate of Interest Questions
- Time Calculation Problems
- Ratio-Based SI Questions
- Percentage Applications
- Advanced Simple Interest Concepts
Example 1: Basic Simple Interest Problem
Question: Find the Simple Interest on ₹5000 at 10% per annum for 3 years.
Solution:
Using formula:
SI = (P × R × T)/100
= (5000 × 10 × 3)/100
= ₹1500
Therefore:
Simple Interest = ₹1500
Example 2: Finding Amount
Question: Find the amount on ₹8000 at 5% per annum for 2 years.
Solution:
Simple Interest:
= (8000 × 5 × 2)/100
= ₹800
Amount:
= Principal + SI
= 8000 + 800
= ₹8800
Therefore:
Amount = ₹8800
Example 3: Finding Principal
Question: A sum amounts to ₹6600 in 2 years at 10% simple interest. Find the principal.
Solution:
Let principal = ₹P
SI:
= (P × 10 × 2)/100
= P/5
Amount:
= P + P/5
= 6P/5
6P/5 = 6600
P = ₹5500
Therefore:
Principal = ₹5500
Example 4: Finding Rate of Interest
Question: A sum of ₹4000 earns ₹1200 as Simple Interest in 4 years. Find the rate of interest.
Solution:
Using formula:
R = (100 × SI)/(P × T)
= (100 × 1200)/(4000 × 4)
= 120000/16000
= 7.5%
Therefore:
Rate of Interest = 7.5% per annum
Example 5: Finding Time
Question: In how many years will ₹3000 amount to ₹4200 at 10% simple interest?
Solution:
SI:
= 4200 − 3000
= ₹1200
Using formula:
T = (100 × SI)/(P × R)
= (100 × 1200)/(3000 × 10)
= 4 years
Therefore:
Time = 4 years
Example 6: Simple Interest for Months
Question: Find the Simple Interest on ₹6000 at 12% per annum for 9 months.
Solution:
Time:
= 9/12 year
= 3/4 year
SI:
= (6000 × 12 × 3)/(100 × 4)
= ₹540
Therefore:
Simple Interest = ₹540
Example 7: Difference Between Amount and Principal
Question: The amount after 3 years is ₹9200 and principal is ₹8000. Find the Simple Interest.
Solution:
SI:
= Amount − Principal
= 9200 − 8000
= ₹1200
Therefore:
Simple Interest = ₹1200
Example 8: Direct Amount Formula
Question: Find the amount on ₹10000 at 8% simple interest for 5 years.
Solution:
Amount:
= P(1 + RT/100)
= 10000(1 + 8 × 5/100)
= 10000(1 + 40/100)
= 10000 × 1.4
= ₹14000
Therefore:
Amount = ₹14000
Example 9: Ratio-Based SI Problem
Question: The Simple Interests on two sums for the same time at the same rate are in the ratio 3 : 5. Find the ratio of principals.
Solution:
For same rate and time:
SI ratio = Principal ratio
Therefore:
Ratio of principals = 3 : 5
Example 10: Finding SI from Amount
Question: The amount on a sum becomes ₹15600 after 4 years at 8% simple interest. If the principal is ₹12000, find the Simple Interest.
Solution:
SI:
= Amount − Principal
= 15600 − 12000
= ₹3600
Therefore:
Simple Interest = ₹3600
Example 11: Equal Interest Concept
Question: Find the Simple Interest on ₹2500 at 12% per annum for 2 years.
Solution:
Yearly interest:
= 12% of 2500
= ₹300
For 2 years:
= 300 × 2
= ₹600
Therefore:
Simple Interest = ₹600
Example 12: Advanced Principal Problem
Question: A sum amounts to ₹16800 in 3 years at 12% simple interest. Find the principal.
Solution:
Amount:
= P(1 + RT/100)
16800 = P(1 + 12 × 3/100)
16800 = P(1 + 36/100)
16800 = 1.36P
P = ₹12352.94
Therefore:
Principal ≈ ₹12352.94
Example 13: Annual Interest Calculation
Question: A person earns ₹900 as Simple Interest in one year at 9% rate. Find the principal.
Solution:
Using formula:
P = (100 × SI)/(R × T)
= (100 × 900)/(9 × 1)
= ₹10000
Therefore:
Principal = ₹10000
Example 14: Mixed Percentage Problem
Question: Find the amount on ₹7500 at 6% simple interest for 4 years.
Solution:
SI:
= (7500 × 6 × 4)/100
= ₹1800
Amount:
= 7500 + 1800
= ₹9300
Therefore:
Amount = ₹9300
Example 15: Advanced Ratio Problem
Question: Two sums invested at the same rate produce Simple Interests of ₹800 and ₹1200 in the same time. Find the ratio of the sums.
Solution:
For same rate and time:
Principal ratio = SI ratio
= 800 : 1200
= 2 : 3
Therefore:
Ratio of sums = 2 : 3
Example 16: Quick SI Percentage Method
Question: Find the Simple Interest on ₹20000 at 5% per annum for 4 years.
Solution:
Total SI percentage:
= 5 × 4
= 20%
SI:
= 20% of ₹20000
= ₹4000
Therefore:
Simple Interest = ₹4000
Important Exam Tips
- Memorize all SI formulas.
- Convert months into years carefully.
- Use direct amount formula for faster solving.
- Use percentage shortcuts wherever possible.
- Differentiate SI and CI clearly.
- Simplify calculations early.
- Verify final answers properly.
Practicing solved examples regularly improves conceptual clarity, logical thinking, and calculation speed in solving Simple Interest questions in competitive examinations.