What Is Input Output Reasoning?
Input output (also called machine input) gives a line of words and/or numbers and shows how a "machine" rearranges it step by step. You find the rule, then answer 5 questions on a new input: a particular step, the position of an element, or the number of steps. It is a regular set in SBI PO, IBPS PO and SBI Clerk mains, RBI Grade B Phase 1 and RRB PO mains.
Key takeaway: Compare the input with Step I and Step II only. Ask: which word moved, which number moved, where did it go, and what order is being built (alphabetical, ascending, descending, by length)? Then write every step of the new input on paper; never jump straight to the last step.
The solved set and practice set below were generated and checked with a Python simulation of the machine, step by step.
Types of Input Output Questions in Bank Exams
| Type | What the machine does | Where it is common |
|---|---|---|
| Word and number arrangement | One word (alphabetical) and one number (ascending or descending) are placed at the ends in each step | SBI PO, IBPS PO mains |
| Pushing (shifting) type | The newly arranged element goes to the extreme end, pushing earlier ones inwards | SBI Clerk / PO mains |
| Calculation based | Numbers are changed (sum of digits, square, difference) in each step | RBI Grade B, IBPS PO mains |
| Interchange / swap | Pairs of elements swap places by a position rule | IBPS Clerk mains |
| Word-letter changes | Letters of words are changed (first letter to next letter, vowels replaced) | SBI PO mains |
How to Solve Input Output Questions (Step-by-Step Trick)
- Find the moved elements. Put Step I under the input and spot what changed position.
- Name the order. Is the word the first in dictionary order? Is the number the largest or smallest?
- Fix the destination. Extreme left, extreme right, or just after the last arranged element?
- Check the pushing rule with Step II: does the new word sit outside the old one (pushing type) or inside it?
- Count steps: with w words and n numbers, the arrangement usually ends in max(w, n) steps, or earlier if some elements are already in place.
- Write each step in full for the new input, then answer all 5 questions from your rough work.
Input Output Solved Example (SBI PO Mains Pattern)
Rule (learned from the sample): in each step, the word that comes first in alphabetical order among the unarranged words moves to the extreme left, and the largest unarranged number moves to the extreme right. Earlier arranged elements are pushed inwards.
Input: 62 tower 18 plane 45 desk 91 rose 33 mango
| Step | Arrangement |
|---|---|
| Input | 62 tower 18 plane 45 desk 91 rose 33 mango |
| Step I | desk 62 tower 18 plane 45 rose 33 mango 91 |
| Step II | mango desk tower 18 plane 45 rose 33 91 62 |
| Step III | plane mango desk tower 18 rose 33 91 62 45 |
| Step IV | rose plane mango desk tower 18 91 62 45 33 |
| Step V | tower rose plane mango desk 91 62 45 33 18 |
Step V is the last step: the words now read in reverse alphabetical order from the left, and the numbers are in descending order.
Questions on this input
- How many steps are needed to complete the arrangement? 5.
- What is the position of "45" from the left in Step II? 6th.
- Which element is 4th from the right in Step III? 33.
- How many elements are between "desk" and "62" in Step IV? 3 (tower, 18, 91).
- In the last step, which element is 3rd to the right of "mango"? 62.
Input Output Tricks for SBI PO and IBPS PO
- Word order in the pushing type comes out reversed. If each new word goes to the extreme left, the last word arranged ends at the far left.
- Numbers: check the first two steps. If Step I takes 91 and Step II takes 62, the rule is "largest first", not "even first".
- Same-letter starts: "desk" and "dose" are ordered by the second letter. Exam inputs usually avoid ties; if they appear, the dictionary rule decides.
- Step-count questions: an element already sitting in its final place can end the arrangement one step early, so always simulate.
- Question asks "which step is this?" Locate how many words are already arranged at the left; that count is the step number.
Common Mistakes in Machine Input Output
- Applying the rule to the sample line instead of the new input.
- Forgetting that a moved element leaves a gap that closes up, so all positions shift by one.
- Counting positions from the wrong end in "4th from the right" questions.
- Assuming a fixed number of steps without writing them out.
Input Output Practice Questions (Same Rule)
Input: sun 27 bat 84 kite 56 ant 39
- What is Step II? Answer: bat ant sun 27 kite 39 84 56.
- Which element is 3rd from the left in Step II? Answer: sun.
- In Step III, which element sits exactly between "27" and "56"? Answer: 84 (Step III: kite bat ant sun 27 84 56 39).
- How many steps complete the arrangement? Answer: 4.
- What is the last step? Answer: sun kite bat ant 84 56 39 27.
Input Output Reasoning FAQs
What is input output in reasoning?
It is a "machine" puzzle where a line of words and numbers is rearranged step by step by a hidden rule; you identify the rule and apply it to a new input.
Is input output asked in SBI PO prelims?
It is mostly a mains topic (SBI PO, IBPS PO, SBI Clerk mains). Prelims rarely include it now, but RRB PO mains and RBI Grade B still do.
How many steps are there in input output questions?
Usually as many as the larger of the number of words and numbers, but the arrangement can finish earlier if elements are already in place. Always simulate.
How do you find the rule in machine input quickly?
Compare the input with Step I and Step II only: note what moved, where it went, and in what order (alphabetical, ascending, descending).
How much time should an input output set take?
Aim for 6–8 minutes for 5 questions in mains: about 3 minutes to decode and write steps, then under a minute per question.
Practice Next
- Mock tests: SBI PO Reasoning Ability Sectional Mock Test 06, IBPS PO Reasoning Ability Sectional Mock Test 05 and SBI PO Inequality, Syllogism and Alphanumeric Series Test 01, plus the mains-level SBI PO Mains Reasoning and Computer Aptitude Sectional Mock Test 01 and IBPS PO Mains Reasoning Ability Sectional Mock Test 01.
- Input output topic tests: SBI PO Input Output Mock Test 01 and SBI Clerk Input Output Mock Test 01, plus the SBI Clerk Mains Reasoning Sectional Mock Test 01.
- Related notes: alphanumeric series tricks for bank exams, word swap questions for bank exams, coded inequality tricks and data sufficiency questions for bank exams.
- Browse all study notes.