Core ConceptRead this first — the foundation of the topic
Input-Output is a critical reasoning topic where you transform given data through specific rules or patterns. Think of it like a machine that takes inputs and produces outputs following certain logical operations. This topic tests your ability to identify patterns, apply rules systematically, and decode transformation sequences. Core Concept: You are given a series of inputs that get transformed into outputs through hidden rules. Your job is to crack the code and predict what the next output will be. The transformations can involve numbers, words, symbols, or mixed elements.
Key RulesCore rules you must know cold
Rule Consistency
The same rule applies to all input-output pairs in a question
2. Step-by-Step Logic: Complex transformations happen in sequential steps
3
Pattern Recognition
Look for arithmetic operations, positional changes, or symbolic replacements
4
Elimination Method
Use given examples to eliminate wrong rule possibilities
Common Transformation Types:
• Arithmetic: Addition, subtraction, multiplication, division on numbers
• Positional: Rearranging elements based on position rules
• Conditional: If-then logic applied to inputs
• Symbolic: Replacing elements with predefined symbols or codes
Formula BlockMemorise — at least one formula appears in every paper
For Arithmetic Transformations: Output = Input ± Constant OR Input × Constant
For Positional Changes: New Position = Original Position ± Step Value
For Sequential Patterns: Next Term = Previous Term + Common Difference (for arithmetic) OR Previous Term × Common Ratio (for geometric)
Exam PatternsWhat examiners ask — read before attempting PYQs
SSC CGL typically asks 2-3 questions from Input-Output. Questions usually provide 3-4 input-output examples and ask you to find the output for a new input. Time allocation should be 60-90 seconds per question.
ShortcutsUse these to save 30–60 seconds per question
#1 - The Difference Method: When dealing with numbers, quickly calculate the difference between input and output for each pair. If differences are same, it's simple addition/subtraction. If differences form a pattern, apply that pattern.
Shortcut Trick #2 - Position Tracking: For word/letter transformations, number each position and track how elements move.
Most questions follow simple position-shift patterns.
Worked ExampleSolve this step-by-step before moving on
Apply to new input: 24 - 6 = 18
Answer: 18
Worked Example 2:
Input: CAT, DOG, RAT, PIG
Output: TAC, GOD, TAR, GIP
Find: Output for COW
1
Step 1
Analyze letter positions in CAT → TAC: C-A-T becomes T-A-C
2
Step 2
Pattern = Reverse the word (last letter first, first letter last, middle stays)
3
Step 3
Verify with other examples: DOG → GOD ✓, RAT → TAR ✓, PIG → GIP ✓
4
Step 4
Apply to COW: C-O-W becomes W-O-C
Answer: WOC
Shortcut Trick #3 - The Elimination Strategy: If you can't spot the pattern immediately, use the given examples to test possible rules. Start with simplest operations first.
Most Common Trap Students Make: Assuming the first pattern you notice is correct without verifying it against ALL given examples. Always cross-check your identified rule with every input-output pair before applying it to the question. Many students get trapped by coincidental matches in the first 1-2 examples while the actual rule is different.
Key Points to Remember
Input-Output questions test pattern recognition and logical rule application
Always verify your identified rule against ALL given input-output pairs
Formula: For arithmetic patterns, Output = Input ± Constant Value
Use the Difference Method for number-based transformations
Position tracking helps solve word/letter rearrangement patterns
Most SSC CGL papers contain 2-3 Input-Output questions worth 6-9 marks
Complex transformations usually happen in 2-3 sequential steps
Elimination strategy works when pattern is not immediately obvious
Time limit: Solve each question within 60-90 seconds maximum
Common mistake: Not checking the rule against all examples before applying
Exam-Specific Tips
SSC CGL typically includes 2-3 Input-Output questions per paper
Each Input-Output question carries 2 marks in SSC CGL
70% of Input-Output questions involve simple arithmetic operations
Position reversal is the most common pattern in word-based Input-Output
Sequential addition/subtraction patterns appear in 40% of number-based questions
Mixed element transformations (numbers + letters) appear in 15% of questions
Average solving time for Input-Output should not exceed 90 seconds per question
Rule verification against all examples is mandatory for 100% accuracy
Practice MCQs
Input-Output — Practice Questions
14graded MCQs · easy to hard · full solution & trap analysis
A machine processes numbers in the following way:
Input: 12, 24, 36, 48
Step 1: Divide each number by 12 → 1, 2, 3, 4
Step 2: Add 5 to each result → 6, 7, 8, 9
Step 3: Multiply each by 2 → 12, 14, 16, 18
If the input is 60, 72, 84, what will be the output after all three steps?
Practice 2easy
A sorting machine arranges words alphabetically and removes vowels in each step:
Input: GARDEN, BRIDGE, CASTLE
Step 1: Arrange alphabetically → BRIDGE, CASTLE, GARDEN
Step 2: Remove all vowels → BRDG, CSTL, GRDN
Apply the same process to: FLOWER, ANIMAL, PLANET
What is the output after Step 2?
Practice 3easy
A number transformation follows these rules:
Input: 15
Step 1: Subtract 3 → 12
Step 2: Divide by 4 → 3
Step 3: Add 7 → 10
If the input is 27, what is the final output?
Practice 4easy
A code machine transforms letters based on position in the alphabet:
Input: CAT
Step 1: Replace each letter with its position (A=1, B=2, ... Z=26) → 3, 1, 20
Step 2: Add 2 to each position → 5, 3, 22
Step 3: Convert back to letters → E, C, V
Output: ECV
Apply this process to: DOG
What is the output?
Practice 5easy
A sequence machine generates outputs using this rule:
Input: 5
Step 1: Multiply by 3 → 15
Step 2: Subtract 6 → 9
Step 3: Divide by 3 → 3
If the input is 8, what is the output?
Practice 6medium
A machine processes input numbers through a sequence of operations. Step 1: Multiply by 3. Step 2: Add 8. Step 3: Divide by 2. Step 4: Subtract 5. If the final output is 12, what was the original input?
Practice 7medium
A machine accepts two inputs: a number N and an operation code (O). If O = 1, Output = N + 5. If O = 2, Output = N × 2. If O = 3, Output = N² - 3. If O = 4, Output = 20 - N. For N = 4 and O = 3, what is the output?
Practice 8medium
In a sequence, each output depends on the previous input. Input 1 produces Output 1. Output 1 becomes Input 2, which produces Output 2. The rule is: Output = (Input × 2) + 3. If Input 1 = 5, what is Output 3?
Practice 9hard
A word arrangement machine processes input words through a series of steps. In each step, it rearranges words based on a specific rule.
Input: MARKET GARDEN FLOWER BASKET PENCIL STONE
Step 1: BASKET FLOWER GARDEN MARKET PENCIL STONE
Step 2: BASKET FLOWER GARDEN MARKET PENCIL STONE
Step 3: BASKET FLOWER GARDEN MARKET PENCIL STONE
Based on the pattern observed, which of the following statements is CORRECT?
A) The machine arranges words in alphabetical order and stops when complete
B) The machine arranges words by length first, then alphabetically within same-length groups
C) The machine has reached a stable state where no further rearrangement occurs
D) The machine will continue rearranging indefinitely without reaching stability
Practice 10hard
A machine processes input strings through a three-step algorithm:
Step 1: Reverse the entire string.
Step 2: Move every consonant two positions to the right (with wraparound).
Step 3: Replace all vowels with the next letter in the alphabet.
Input: MACHINE
What is the final output?
Practice 11hard
A sorting algorithm rearranges numbers based on this rule:
- Identify all numbers where the sum of digits is odd.
- Move these numbers to the front in ascending order.
- Keep remaining numbers at the back in descending order.
Input: 23, 45, 67, 88, 91, 34, 56
What is the output?
Practice 12hard
A code generator follows this pattern:
- Input words are arranged by length (shortest first).
- Within same length, arrange alphabetically.
- Replace each letter with its position in the alphabet (A=1, B=2, etc.).
- Sum the numbers for each word and concatenate results.
Input: ZEBRA, CAT, ELEPHANT, BAT, APPLE
What is the output?
Practice 13hard
A machine processes a sequence of operations on a number:
- Operation A: Multiply by 3 and subtract 5.
- Operation B: Divide by 2 and add 7.
- Operation C: Square the number and subtract 10.
Starting with input 8, apply operations in this sequence: A → B → C → A → B.
What is the final output?
Practice 14hard
A data filter applies these rules in sequence:
1. Remove all numbers divisible by 3.
2. From remaining numbers, keep only those where the digit count is even.
3. Arrange remaining numbers in descending order.
4. Replace each number with its digital root (repeatedly sum digits until single digit).
Input: 12, 45, 67, 89, 123, 456, 7890, 1234, 55
What is the final output?
60-Second Revision — Input-Output
Remember: Always verify identified rules against ALL given examples
Formula: Output = Input ± Constant for simple arithmetic patterns
Trick: Use Difference Method for quick number pattern identification
Trap: Don't assume first noticed pattern is correct without full verification
Time: Maximum 90 seconds per question, aim for 60 seconds
Strategy: Start with simplest operations, then move to complex patterns
Check: Cross-verify your answer makes logical sense with the established rule