Input-Output
Input-Output (Machine Rearrangement)
A machine receives a line of words and/or numbers as input and rearranges them across steps. You are shown some intermediate steps and asked to identify a specific step, the number of total steps, or the content of a given step.
Key Idea
Study at least two consecutive steps to reverse-engineer the machine's rule before answering — the rule is fixed and applies identically at every step.
Core Rules
Rule Detection from Two Steps
Compare Step 1 to Step 2: identify which element moved, where it went, and how the rest shifted; confirm the same rule holds from Step 2 to Step 3
Always — as the very first action before attempting any question about the input-output sequence.
Dual-End Arrangement Rule
Many machines move the largest/smallest number to the left end AND the alphabetically first/last word to the right end in alternate sub-steps within one step
When both numbers and words are present and each step seems to place two elements simultaneously.
Counting Total Steps
Total steps = number of elements ÷ elements placed per step (round up for odd elements); the sequence terminates when all elements are in sorted order
When the question asks 'In how many steps will the arrangement be complete?'
Backward Tracing
To find an earlier step from a later one, reverse the machine's rule: un-sort the last placed element and shift the remainder back to their prior positions
When only the final or a late step is given and you need to find the input or an earlier intermediate step.
Position Anchoring
Once an element is placed at its final position in any step, it never moves again in subsequent steps; use this to anchor known positions and reduce the search space
When reconstructing any specific step — check which elements have already been anchored in prior steps.
Relevant Exams
Input-Output appears as a full puzzle set (4–5 questions) in almost every IBPS PO and SBI PO mains paper. Mastering rule detection can earn all 4–5 marks in under 3 minutes.