Study Material — 16 PYQs (2019–2019) · Concept Notes · Shortcuts
SSC MTS Difference SI vs CI is a frequently tested subtopic — 16 previous year questions from 2019–2019 papers are included below with concept notes, key rules and shortcut tricks.
16 questions from actual SSC MTS papers · all shown free · click option to reveal solution
Exam Q 12019Previous Year Pattern
The difference between compound interest and simple interest on ₹4,000 for 2 years is ₹40. What is the rate of interest per annum?
Exam Q 22019Previous Year Pattern
A sum of ₹5,000 is invested at 10% per annum for 2 years. What is the difference between the compound interest and simple interest earned?
Exam Q 32019Previous Year Pattern
₹8,000 is lent at 5% per annum compound interest. The difference between CI and SI for 3 years is ₹61. What is the compound interest for 3 years?
Exam Q 42019Previous Year Pattern
A principal amount earns ₹400 as simple interest in 2 years at 8% per annum. If the same principal is invested at 8% compound interest for 2 years, how much more interest will be earned?
Exam Q 52019Previous Year Pattern
The difference between compound interest and simple interest on a sum for 2 years at 12% per annum is ₹144. What is the principal?
Exam Q 62019Previous Year Pattern
A sum of ₹6,000 is invested at 15% per annum. The simple interest for 1 year is ₹900. If the same sum is invested at compound interest for 1 year at the same rate, what is the difference between CI and SI?
Exam Q 72019Previous Year Pattern
The simple interest on a sum for 2 years at 6% per annum is ₹480. If the same sum is invested at 6% compound interest for 2 years, how much more interest will be earned compared to simple interest?
Exam Q 82019Previous Year Pattern
A sum of ₹8,000 is invested at 10% per annum. What is the difference between the compound interest and simple interest earned over 2 years?
Exam Q 92019Previous Year Pattern
A principal amount earns ₹500 as simple interest in 2 years at 5% per annum. If the same principal is invested at 5% compound interest for 2 years, what is the compound interest earned?
Exam Q 102019Previous Year Pattern
The difference between compound interest and simple interest on a sum for 3 years at 8% per annum is ₹245.76. Find the principal.
Exam Q 112019Previous Year Pattern
A sum becomes ₹1,210 in 2 years and ₹1,331 in 3 years under compound interest. What is the rate of interest per annum?
Exam Q 122019Previous Year Pattern
A person invests ₹6,400 at 12.5% per annum compound interest. After how many years will the amount become ₹10,240?
Exam Q 132019Previous Year Pattern
A sum of money becomes ₹4,840 in 2 years at 10% per annum under simple interest. What will be the difference between compound interest and simple interest on the same principal for the same period and rate?
Exam Q 142019Previous Year Pattern
A principal amount is invested at 8% per annum. The difference between compound interest for 2 years and simple interest for 2 years is ₹51.20. If the same principal is invested at 6% per annum for 3 years under compound interest, what will be the compound interest earned?
Exam Q 152019Previous Year Pattern
The compound interest on a sum for 2 years at 10% per annum exceeds the simple interest on the same sum for the same period and rate by ₹100. What is the principal? Additionally, if this principal is invested at 12% per annum compound interest for 2 years, what will be the total amount?
Exam Q 162019Previous Year Pattern
Two equal sums are invested at the same rate of interest per annum for 2 years. One sum is invested under simple interest and the other under compound interest. If the difference between the amounts received is ₹40, and the rate of interest is 10% per annum, what is each sum?
Concept Notes
Difference SI vs CI— Rules & Concept
Core ConceptRead this first — the foundation of the topic
The difference between Simple Interest (SI) and Compound Interest (CI) is one of the most frequently tested concepts in SSC CGL. This difference exists because compound interest includes interest on previously earned interest, while simple interest does not. Core Concept:
Simple Interest is calculated only on the principal amount throughout the investment period. Compound Interest is calculated on the principal plus accumulated interest from previous periods. The difference between CI and SI represents the 'extra earning' due to compounding effect.
Formula BlockMemorise — at least one formula appears in every paper
For 2 years: CI - SI = P × R² / (100)²
For 3 years: CI - SI = P × R² × (300 + R) / (100)³
Where P = Principal, R = Rate per annum, T = Time
Exam PatternsWhat examiners ask — read before attempting PYQs
SSC CGL typically asks three types of questions
(1) Direct calculation of difference given P, R, T (2) Finding principal when difference and rate are given (3) Finding rate when principal and difference are given. Most questions involve 2-3 years timeframe as longer periods make calculations complex
Powerful Shortcut for 2 Years
Difference = (SI for 1 year)² / Principal
This works because: If SI for 1 year = PRT/100, then difference = (PRT/100)² / P = PR²T²/(100²P) = PR²/100² (for T=2)
Worked ExampleSolve this step-by-step before moving on
1
Step 1
Calculate SI for 2 years
SI = (P × R × T) / 100 = (8000 × 15 × 2) / 100 = Rs. 2400
2
Step 2
Calculate CI for 2 years
Amount = P(1 + R/100)ᵀ = 8000(1 + 15/100)² = 8000 × (1.15)² = 8000 × 1.3225 = Rs. 10,580
CI = Amount - Principal = 10,580 - 8000 = Rs. 2580
3
Step 3
Find difference
CI - SI = 2580 - 2400 = Rs. 180
Alternative (Using Formula):
CI - SI = P × R² / (100)² = 8000 × (15)² / (100)² = 8000 × 225 / 10000 = Rs. 180
ShortcutsUse these to save 30–60 seconds per question
for 3 Years:
For 3 years, the difference equals: 3 × (2-year difference) + (2-year difference × R/100)
Exam TrapsCommon mistakes students make — avoid these
Students often confuse the formula for different time periods. Remember: the 2-year formula is simplest and most tested. For 3 years, don't memorize the complex formula - use the relationship with 2-year difference instead.
Key Points to Remember
Difference exists only when time period is more than 1 year
For 2 years: CI - SI = P × R² / (100)²
For 3 years: CI - SI = P × R² × (300 + R) / (100)³
Difference represents interest earned on interest portions
2-year difference problems are most common in SSC CGL
If SI for 1 year is known, 2-year difference = (SI)² / Principal
Compound Interest is always greater than Simple Interest for same P, R, T
The difference increases exponentially with higher rates and longer periods
Exam-Specific Tips
For 2 years at 10% rate, difference is always 1% of principal
For 2 years at 20% rate, difference is always 4% of principal
For Rs. 100 at 15% for 2 years, difference is exactly Rs. 2.25
The ratio CI:SI for 2 years at 10% is always 21:20
For 3 years, minimum additional factor in formula is 300 (when R=0)
Difference for 2 years = P×R²/10000 (direct calculation)
For equal principal and rate, 3-year difference is roughly 3 times 2-year difference
At 25% rate for 2 years, difference equals 6.25% of principal
60-Second Revision — Difference SI vs CI
Formula: 2 years difference = P × R² / 10000
Remember: Difference exists only when T > 1 year
Trick: 2-year difference = (Annual SI)² / Principal
Pattern: Most SSC questions use 2-3 year timeframes
Trap: Don't use 3-year formula for 2-year problems
Quick check: At 10% for 2 years, difference = 1% of principal
Method: Calculate both CI and SI separately when formulas confuse