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Input-Output & Machine Coding for IBPS PO

Master machine input-output problems with step-by-step methods, pattern recognition tricks, and solved examples. Learn to solve 5 questions quickly in the Reasoning section.

What is Input-Output in Reasoning?

Input-Output (also called Machine Coding or Machine Input-Output) is an important topic in the IBPS PO Reasoning section. Typically, 5 questions are asked from this topic in Mains exam, and sometimes in Prelims as well.

In these questions, you are given an input (a set of words, numbers, or both) and a series of steps showing how the machine rearranges the input step by step. You need to identify the pattern or logic behind the rearrangement and then answer questions based on that pattern.

Why this topic matters: Once you understand the pattern, input-output questions become very predictable and scoring. With practice, you can solve 5 questions in under 5 minutes.

Types of Input-Output Patterns

  • Shifting Pattern: Elements are shifted to left or right based on a specific rule (e.g., smallest number, largest word).
  • Arrangement Pattern: Elements are arranged in ascending/descending order of numbers or alphabetical order of words.
  • Operation Based Pattern: Numbers are modified by mathematical operations (addition, subtraction, multiplication, division).
  • Mixed Pattern: Combination of shifting and arrangement (e.g., numbers arranged in one step, words in another).
  • Double Shifting Pattern: Two elements are processed in each step (one from left, one from right).

Step-by-Step Approach to Solve Input-Output

Step 1: Observe the Input and Output Steps

Look at the given input and each subsequent step. Identify what changes from one step to the next.

Step 2: Identify the Pattern

Check whether numbers are being arranged (ascending/descending) or words (alphabetical order). Also check if shifting is happening (moving elements to left or right).

Step 3: Note the Direction

Are elements being moved from left to right, right to left, or both? Is the machine processing one element per step or two elements?

Step 4: Verify Pattern with All Steps

Check if your identified pattern works for all given steps. If yes, you can predict further steps or answer questions.

Step 5: Answer Questions

Questions typically ask: "What is the nth step?", "What is the position of X in step Y?", "What comes between A and B in step Z?"

Shortcut Tricks for Input-Output

Trick 1: Don't Solve All Steps

If the question asks for a later step (e.g., Step 5), don't write all previous steps. Identify the pattern and directly compute the required step.

Trick 2: Track One Element

Follow the movement of a single element across steps. This helps understand the shifting rule quickly.

Trick 3: Look for Numbers vs Words Separately

If input has both numbers and words, they are often processed separately or with different rules.

Trick 4: Reverse Engineering

If multiple steps are given, sometimes it's easier to work backwards from the final step to understand the pattern.

Solved Example 1: Shifting Pattern

Question:

Input: 83 56 41 97 62 35 78
Step 1: 35 83 56 41 97 62 78
Step 2: 35 41 83 56 62 97 78
Step 3: 35 41 56 83 62 78 97
Step 4: 35 41 56 62 83 78 97
Step 5: 35 41 56 62 78 83 97
Step 6: 35 41 56 62 78 83 97
Question: What is the position of 83 in Step 3?

Solution:

Step 1 - Identify pattern: Looking at the steps, the smallest number (35) moves to the leftmost position in Step 1. Then the next smallest (41) moves to second position in Step 2. The pattern is: In each step, the next smallest remaining number is picked and placed at the left in its correct sorted position. This is an ascending order arrangement from left.

Step 2 - Find position in Step 3: Step 3 is: 35 41 56 83 62 78 97. Here 83 is at the 4th position (counting from left, position 4).

Answer: 83 is at 4th position in Step 3.

Solved Example 2: Word Arrangement

Question:

Input: cat dog apple bat elephant fan
Step 1: apple cat dog bat elephant fan
Step 2: apple bat cat dog elephant fan
Step 3: apple bat cat dog elephant fan
Step 4: apple bat cat dog elephant fan
Step 5: apple bat cat dog elephant fan
Question: How many steps are required to complete the arrangement?

Solution:

Step 1 - Identify pattern: The words are being arranged in alphabetical order from left to right. "apple" comes first alphabetically, then "bat", then "cat", then "dog", then "elephant", then "fan".

Step 2 - Check completion: At Step 2, the arrangement is: apple bat cat dog elephant fan. This is fully alphabetically sorted. Steps 3, 4, 5 are the same (no change). So arrangement completes at Step 2.

Answer: 2 steps are required to complete the arrangement.

Solved Example 3: Number Operation Pattern

Question:

Input: 12 8 5 15 20 3
Step 1: 6 8 5 15 20 3
Step 2: 6 4 5 15 20 3
Step 3: 6 4 5 7.5 20 3
Step 4: 6 4 5 7.5 10 3
Step 5: 6 4 5 7.5 10 1.5
Question: What is the operation performed in each step?

Solution:

Observation: Step 1: 12 becomes 6 (half of 12). Step 2: 8 becomes 4 (half of 8). Step 3: 15 becomes 7.5 (half of 15). Step 4: 20 becomes 10 (half of 20). Step 5: 3 becomes 1.5 (half of 3).

Pattern: In each step, the machine takes the leftmost undivided number and divides it by 2. It processes one number per step from left to right.

Answer: Each step divides the next number by 2.

Practice Questions for Self-Assessment

Practice Question 1:

Input: 45 22 67 34 89 53
Step 1: 22 45 67 34 89 53
Step 2: 22 34 45 67 89 53
Step 3: 22 34 45 53 67 89
Step 4: 22 34 45 53 67 89
Question: What is the position of 67 in Step 3?

Practice Question 2 (Words):

Input: zebra yellow mango apple grape orange
Step 1: apple zebra yellow mango grape orange
Step 2: apple grape zebra yellow mango orange
Step 3: apple grape mango zebra yellow orange
Step 4: apple grape mango orange zebra yellow
Step 5: apple grape mango orange yellow zebra
Question: How many steps are needed to complete the alphabetical arrangement?

Practice Question 3 (Operation):

Input: 7 14 21 28 35
Step 1: 7 7 21 28 35
Step 2: 7 7 14 28 35
Step 3: 7 7 14 14 35
Step 4: 7 7 14 14 17.5
Question: What is the operation pattern?

Answers: Q1: 5th position | Q2: 5 steps | Q3: Each step halves the next number from the right

Frequently Asked Questions about Input-Output

Q1: How many questions come from Input-Output in IBPS PO?
Typically, 5 questions are asked from Input-Output in the Mains exam. Sometimes 3-5 questions appear in Prelims as well.
Q2: What is the most common pattern in Input-Output?
The most common patterns are: ascending/descending arrangement of numbers, alphabetical arrangement of words, and shifting of smallest/largest element to one end.
Q3: How can I solve input-output questions faster?
Don't write all steps. Identify the pattern in 2-3 steps, then directly determine the required step without writing intermediate steps.
Q4: What is double shifting in input-output?
Double shifting means the machine processes two elements in each step: one from the left end and one from the right end simultaneously.
Q5: Can input-output questions have mathematical operations?
Yes, sometimes numbers are modified by operations like addition, subtraction, multiplication, division, or finding squares/roots.
Q6: What if the machine stops before sorting completely?
Some questions have a fixed number of steps. The pattern continues in the same manner until the specified step.

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