Core ConceptRead this first — the foundation of the topic
CORE CONCEPT — WHAT IS INPUT-OUTPUT? Input-Output is a machine-based logic puzzle. A machine takes a line of words or numbers (called INPUT). It rearranges them step by step. Each step follows a fixed hidden rule. Your job is to find that rule and answer questions about any step.
Think of it like a washing machine. You put dirty clothes in (input). Each cycle does something. After all cycles, you get clean, arranged clothes (output). ---
Key RulesCore rules you must know cold
1
The rule is ALWAYS consistent. Every step follows the same pattern.
2
The arrangement can involve words, numbers, or both.
3
Common operations: shifting words/numbers left or right, arranging in ascending or descending order, alternating between smallest and largest, arranging alphabetically.
4
The machine usually completes in 4 to 6 steps.
5
Once an element is placed in its final position, it does NOT move again in later steps.
Exam PatternsWhat examiners ask — read before attempting PYQs
Question types
- What is Step 3 of the given input?
- Which step gives a particular output?
- How many steps are needed to complete the arrangement?
- What is the position of a specific word in a given step?
- Which step is the final output?
---
TYPES OF INPUT-OUTPUT MACHINES
Type 1 — Word Shift Machine: Words move one by one to the left or right end
Type 2 — Number Arrangement
Numbers arrange in ascending or descending order, one number per step
Type 3 — Alternating Arrangement
Smallest number goes to the left end, largest goes to the right end, alternating in each step
Type 4 — Word plus Number Mix
Words and numbers are arranged separately — words alphabetically, numbers in order.
---
Formula BlockMemorise — at least one formula appears in every paper
Shortcut 1 — Count Elements to Find Total Steps:
If there are N elements and 1 element gets fixed per step, total steps = N minus 1.
Example: 6 elements = 5 steps maximum.
Shortcut 2 — Alternating Type Formula:
If smallest goes LEFT and largest goes RIGHT alternately:
Step 1 = smallest fixed at left
Step 2 = largest fixed at right
Step 3 = second smallest fixed at left
Step 4 = second largest fixed at right
...and so on.
So for 6 elements, after 5 steps, the arrangement is complete.
Shortcut 3 — Identify the Rule in 2 Steps:
Always look at Step 1 and Step 2 carefully before doing anything else. The rule becomes 100 percent clear by Step 2. Never guess from Step 1 alone.
---
Worked ExampleSolve this step-by-step before moving on
1
Step 1
8 45 13 72 29 56
2
Step 2
8 13 45 72 29 56
3
Step 3
8 13 29 45 72 56
4
Step 4
8 13 29 45 56 72
Final output after 4 steps: 8 13 29 45 56 72 (ascending order)
Question: What is Step 2?
Answer: 8 13 45 72 29 56
Step-by-step logic: In each step, the next smallest number from the remaining unsorted elements shifts to the correct position. Track fixed elements (underline them mentally).
---
WORKED EXAMPLE 2 — ALTERNATING WORD AND NUMBER
Input: mango 32 apple 17 kite 54
Rule: In odd steps, the word that comes first alphabetically moves to the leftmost position. In even steps, the largest number moves to the rightmost position.
1
Step 1
apple mango 32 17 kite 54
2
Step 2
apple mango 32 17 kite 54 — wait, 54 is already at the right.
Let us re-read: 54 moves to the right end.
2
Step 2
apple mango 32 17 kite 54
3
Step 3
apple kite mango 32 17 54
4
Step 4
apple kite mango 17 32 54
5
Step 5
apple kite mango 17 32 54 — arrangement complete.
Key learning: Always re-check if an element is already in position. Do not count it as a new step.
---
Exam TrapsCommon mistakes students make — avoid these
— NUMBER 1 TRAP
Students assume the rule from Step 1 only and apply it wrong.
Example trap: In Step 1, the smallest number moves left. Student assumes smallest always moves. But from Step 2, the rule shifts to largest moving right.
This alternating rule is the most common trap in SSC CGL input-output questions.
FIX: Always verify the rule using BOTH Step 1 and Step 2 before solving.
Also, students forget that already-fixed elements stay in place. They re-arrange them by mistake and get the wrong step output.
---
EXAM STRATEGY
1. Read the full input and all given steps before answering.
2.
Write down Step 1 and Step 2 and find the pattern.
3. Use the total-steps formula to estimate how many steps remain.
4. Answer all 4-5 questions from the same pattern — saves huge time.
5.
Target: Solve the full set in 3 to 4 minutes maximum.
Key Points to Remember
Input-Output involves a machine rearranging words or numbers step by step using a fixed hidden rule.
The rule NEVER changes between steps — it stays consistent throughout the entire process.
Formula: If N elements are given and 1 is fixed per step, maximum steps = N minus 1.
Shortcut: Always identify the rule by studying Step 1 AND Step 2 together, never from Step 1 alone.
Alternating rule pattern: Smallest goes to left end in odd steps, largest goes to right end in even steps.
Once an element is placed in its final position, it does not move in any later step.
Types asked in SSC CGL: number ascending/descending, alphabetical word order, alternating, and mixed word-number.
Shortcut: For alternating arrangement with 6 elements, the machine finishes in exactly 5 steps.
Trap: Never assume alternating rule stops — it continues until all elements are arranged.
Exam strategy: Crack the rule first, then answer all 4-5 questions at once to save time.
Exam-Specific Tips
SSC CGL typically sets 4 to 5 questions from a single Input-Output problem in the Tier-1 paper.
The most common Input-Output type in recent SSC CGL papers is the Alternating Arrangement — smallest to left, largest to right.
If 7 elements are given in an input, the maximum number of steps to reach the final output is 6.
In a pure ascending number arrangement machine, Step 1 always places the smallest number at position 1.
In a descending arrangement machine, Step 1 always places the largest number at position 1.
The final output step is the step where no further rearrangement is possible — all elements are in their target positions.
Mixed input-output problems (words + numbers) in SSC CGL usually arrange words alphabetically and numbers in ascending or descending order simultaneously.
Practice MCQs
Input-Output — Practice Questions
37graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 37
A word processing machine processes words following a specific rule. Study the pattern:
Input: MOTHER FATHER SISTER
Step 1: REHTOM REHTAF RETSIS
Step 2: REHTOM4 REHTAF6 RETSIS6
Step 3: 4REHTOM 6REHTAF 6RETSIS
Following the same rule, what will be Step 3 for the input: BROTHER?
A) 7REHTORB
B) REHTORB7
C) 7REHTOB
D) REHTORB
Practice 2easy
A sorting machine arranges numbers in ascending order, but with a special rule:
First, separate odd and even numbers.
Then, arrange odds in ascending order, then evens in ascending order.
Finally, place all odds before all evens.
Input: 7, 2, 9, 4, 1, 6
What is the output?
Practice 3easy
A code machine encodes words using this pattern:
A=1, B=2, C=3, ..., Z=26
Each letter's code is multiplied by its position in the word.
For the word CAT:
C (position 1) = 3 × 1 = 3
A (position 2) = 1 × 2 = 2
T (position 3) = 20 × 3 = 60
Total code = 3 + 2 + 60 = 65
What is the code for the word BAT?
Practice 4easy
A word arrangement machine processes input words through a series of steps. Study the pattern:
Input: MOTHER FATHER SISTER BROTHER
Step 1: FATHER MOTHER SISTER BROTHER
Step 2: FATHER SISTER MOTHER BROTHER
Step 3: FATHER SISTER BROTHER MOTHER
Following the same logic, what will be the arrangement after Step 2 if the input is: APPLE BANANA CHERRY DATE?
Practice 5easy
A number processing machine follows these rules:
Rule 1: If the number is even, divide by 2.
Rule 2: If the number is odd, multiply by 3 and add 1.
Rule 3: Repeat until you reach 1.
Starting with 10, how many steps does it take to reach 1?
Practice 6easy
A sequence machine generates numbers using this rule:
Start with 2.
Each step: Multiply the previous number by 2, then subtract 1.
Step 1: 2 × 2 − 1 = 3
Step 2: 3 × 2 − 1 = 5
Step 3: 5 × 2 − 1 = 9
What is the number at Step 5?
Practice 7medium
A number processing system follows these rules:
- If the number is even, divide by 2
- If the number is odd, multiply by 3 and add 1
- Stop when you reach 1
Starting with 18, how many operations are needed to reach 1?
Practice 8medium
A sequence machine produces outputs following a specific pattern:
Input: 5 → Output: 26
Input: 8 → Output: 65
Input: 3 → Output: 10
Input: 7 → Output: 50
Based on this pattern, what will be the output for Input: 6?
Practice 9medium
A logic gate system processes binary inputs with the following rules:
- Input pair (1,1) → Output 0
- Input pair (1,0) → Output 1
- Input pair (0,1) → Output 1
- Input pair (0,0) → Output 0
If three inputs are processed sequentially (first two inputs produce an intermediate output, which is then paired with the third input), what will be the final output for inputs 1, 0, 1 (in that order)?
Practice 10medium
A machine processes input numbers through the following steps:
Step 1: Multiply the input by 3
Step 2: Add 5 to the result
Step 3: Divide by 2
Step 4: Subtract the original input
If the input is 10, what is the final output?
Practice 11medium
A machine processes input numbers through the following steps:
Step 1: Multiply the number by 3
Step 2: Add 5 to the result
Step 3: Divide by 2
Step 4: Subtract the original number
If the input is 10, what is the final output?
Practice 12medium
A device processes input according to these conditions:
- If the number is even, divide by 2
- If the number is odd, multiply by 3 and add 1
- Repeat until the result is 1
- Count the total number of operations performed
How many operations are needed to reduce 10 to 1?
Practice 13medium
A word arrangement machine processes input words in a specific pattern. When given the input 'MACHINE LEARNING SYSTEMS WORK', the machine rearranges them in the following steps:
Step 1: WORK MACHINE LEARNING SYSTEMS
Step 2: WORK SYSTEMS MACHINE LEARNING
Step 3: WORK SYSTEMS LEARNING MACHINE
Step 4: WORK SYSTEMS LEARNING MACHINE
Following the same logic, if the input is 'DIGITAL TRANSFORMATION ENABLES GROWTH', what will be the arrangement in Step 2?
Practice 14medium
A coding machine converts letters based on their position in the alphabet. The rule is: each letter shifts forward by a number equal to its position (A=1, B=2, etc.). For example, A (position 1) becomes B, C (position 3) becomes F.
What will be the code for the word 'CAB'?
Practice 15medium
A sequence of numbers follows this pattern:
Input: 8, 12, 16, 20, 24
Output: 3, 5, 7, 9, 11
Based on this pattern, if the input is 32, what will the output be?
Practice 16medium
In a coding system, words are transformed as follows:
- Reverse the word
- Replace each vowel with the next letter in the alphabet
- Shift each consonant 2 positions forward in the alphabet
What is the output for the word 'MAKE'?
Practice 17medium
A machine processes input through these rules:
Rule 1: If the number is divisible by 3, multiply by 2
Rule 2: If the number is divisible by 5, subtract 3
Rule 3: If the number is divisible by both 3 and 5, apply Rule 1 first, then Rule 2
What is the output for input 30?
Practice 18medium
A device processes numbers through these operations (in order):
1. Add 8
2. Multiply by 2
3. Subtract 6
4. Divide by 4
If the output is 5, what was the input?
Practice 19medium
A machine processes input numbers through the following steps:
Step 1: Multiply the number by 3
Step 2: Add 5 to the result
Step 3: Divide by 2
Step 4: Subtract the original number
If the input is 10, what is the final output?
Practice 20medium
A sequence follows this pattern:
Input: A series of numbers
Step 1: Arrange in ascending order
Step 2: Remove all even numbers
Step 3: Add 1 to each remaining number
Step 4: Calculate the sum of all results
For input {15, 8, 23, 12, 7, 19}, what is the final output?
17 more practice questions in the Study Panel
Difficulty-graded, bookmarkable, with timed mode. Free account — no credit card.