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Question

You have four puzzle books on your shelf, and you decide to arrange them in every possible order, moving one book every 30 seconds. How long will it take to arrange all the books?

This question was previously asked in
SSC Stenographer 2025 Question Paper (06-Aug-2025) Shift 2
The correct answer is

12 minutes

Arrangement Possibilities Explained

The problem asks us to determine the total time required to arrange four distinct puzzle books on a shelf in every possible order. We are given that each unique arrangement takes 30 seconds to complete.

Permutations Calculation for Arrangements

To find out how many different ways the four books can be arranged, we need to calculate the number of permutations of these four books. The formula for permutations of 'n' distinct items is \(n!\) (n factorial).

In this case, we have 4 books, so \(n=4\). The total number of possible arrangements is:

\(4! = 4 \times 3 \times 2 \times 1\)

Calculating this value:

\(4! = 24\)

This means there are 24 different ways to arrange the four puzzle books on the shelf.

Time Calculation for All Arrangements

We know that each of these 24 arrangements takes 30 seconds. To find the total time, we multiply the number of arrangements by the time taken for each arrangement.

Total Time (in seconds) = Number of Arrangements \(\times\) Time per Arrangement

\(\text{Total Time} = 24 \times 30 \text{ seconds}\)

\(\text{Total Time} = 720 \text{ seconds}\)

Conversion to Minutes

The question asks for the time in minutes. Since there are 60 seconds in one minute, we need to convert the total time from seconds to minutes.

Total Time (in minutes) = Total Time (in seconds) \(\div\) 60

\(\text{Total Time} = \frac{720 \text{ seconds}}{60 \text{ seconds/minute}}\)

\(\text{Total Time} = 12 \text{ minutes}\)

Therefore, it will take 12 minutes to arrange all four puzzle books in every possible order.

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Important Questions from Permutation and Combination

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  3. In a tournament of Chess having 150 entrants, a player is eliminated whenever he loses a match. It is given that no match results in a tie/draw. How many matches are played in the entire tournament?

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