Input Output Reasoning: Machine Input Output Types, Steps, Tricks and Solved Examples for SSC CGL and CHSL

In input output reasoning, a machine takes an input line of words or numbers and changes it step by step by following a fixed rule, until the final arrangement (output) is reached. You have to find the rule, and then answer questions about a particular step or the final output. This guide on input output reasoning for SSC explains the types, the method of finding the rule, the number of steps, and solved examples with practice questions and FAQs.

Types of Input Output Questions

Step-by-Step Method

1. Compare the input with Step I and note exactly what has changed.
2. Compare Step I with Step II to confirm the rule.
3. Find out whether the rule is about position, order or an operation.
4. Write the rule in your own words, for example “the smallest number goes to the left end”.
5. Apply the rule to the new input, or work out the required step directly.

Number of Steps

• If one element is placed in its final position in each step, the number of steps for n elements = n − 1 (the last element falls into place automatically).
• If two elements are placed in each step, the steps are about n/2.
• The last step is the one in which the output equals the final arrangement.

Solved Examples

Example 1 (words). Input: sun moon star cloud rain.
Rule: the word that comes first alphabetically among the rest goes to the next place from the left.
Step I: cloud sun moon star rain
Step II: cloud moon sun star rain
Step III: cloud moon rain sun star
Step IV: cloud moon rain star sun. This is the output, reached in 4 steps (n − 1 = 4).

Example 2 (numbers). Input: 84 29 57 13 66. The smallest number of the remaining moves to the left end of the unsorted part in each step.
Step I: 13 84 29 57 66
Step II: 13 29 84 57 66
Step III: 13 29 57 84 66
Step IV: 13 29 57 66 84 (final).

Example 3 (operation). Input: 14 9 22 5. Rule: odd numbers increase by 3 and even numbers decrease by 2.
Output: 12, 12, 20, 8.

Example 4. For the input of Example 2, what will be Step III?
13 29 57 84 66.

Example 5. Input: zebra lion goat deer. With the rule of Example 1, find Step II.
Step I: deer zebra lion goat. Step II: deer goat zebra lion.

Tricks

• Look at the first and last elements first, because they usually show the rule quickly.
• If the elements of the input and the output are the same, the rule is about position or order; if they differ, an operation is applied.
• Count the steps from the rule, not by redoing all steps.
• For alphabetical rules, write the final alphabetical order first and fill the steps from it.
• Keep a rough table of Step I, II and III while practising.

Quick Tips

• Compare Step I with the input to find the rule.
• Write the final order first for alphabetical rules.
• Use n − 1 for the number of steps in one-by-one sorting.
• Check the rule on Step II before applying it to the question.

Quick Revision Points

• Shifting types move one element per step.
• Steps in one-by-one sorting = n − 1.
• Operation types change each number by a fixed rule.
• Find the rule by comparing the input with Step I and Step I with Step II.
• The output is the last step of the machine.

Practice Questions With Answers

1. If a machine sorts 5 words one at a time, how many steps are needed?
   Answer: 4 steps
2. Input: 48 21 63 9 35. The smallest of the remaining numbers goes to the left in each step. Find Step II.
   Answer: 9 21 48 63 35
3. For the same input, find Step IV (final).
   Answer: 9 21 35 48 63
4. Input: 15 72 40 8 25. The largest of the remaining goes to the left. Find Step II.
   Answer: 72 40 15 8 25
5. Rule: odd numbers +3 and even numbers −2. Input: 10 7 12 5. Find the output.
   Answer: 8 10 10 8
6. How many steps are needed to arrange 9 words one at a time?
   Answer: 8 steps
7. Input: 52 18 77 31 (smallest to the left). Find Step I.
   Answer: 18 52 77 31
8. Input: zebra lion goat deer (alphabetical, first goes left). Find Step II.
   Answer: deer goat zebra lion
9. Rule: numbers less than 10 are doubled, others reduced by 5. Input: 6 14 9 20. Find the output.
   Answer: 12 9 18 15
10. Which type of input output changes the numbers by a fixed rule?
    Answer: Mathematical operation type

How to Practise This Chapter

Practise 10 questions every day and write the steps on paper. Then attempt timed sets from our practice papers and the previous year papers page. See all topics on the Reasoning notes page and the next topic Alphanumeric Series.

Frequently Asked Questions

What is input output reasoning?

It is a reasoning topic in which a machine changes an input line by a fixed rule in steps and you answer questions about the steps or the output.

How do I find the rule in input output questions?

Compare the input with Step I and Step I with Step II, and note what moves or changes.

How many steps are needed to sort n elements one by one?

n − 1 steps.

What are the types of input output questions?

Shifting, alphabetical arrangement, number arrangement, mathematical operation and mixed types.

Is input output asked in SSC CGL?

It is more common in banking exams, but SSC CGL, CHSL and other exams also include it in reasoning.

How much time should I take?

About 60 to 90 seconds per set.

What is the last step?

The step in which the arrangement matches the final output.

How do I handle words and numbers together?

Find the rule for words and the rule for numbers separately.

What if the rule is not clear from Step I?

Check Step II as well, because two steps usually confirm the rule.

Can I solve without writing all the steps?

Yes, if the rule is clear you can jump to the required step directly.

What is an operation-based input output?

A type in which each element is changed by a mathematical operation like add, subtract or multiply.

What are common mistakes?

Finding the rule from only one step and miscounting the number of steps.