Question

Four books, one English, one science, one social science, and one mathematics, are to be arranged in the shelf. In how many ways this can be done?

• A. $6$
• B. $4!$
• C. $5!$
• D. $36$

Answer 1

The correct option is B $4!$

We know that the number of permutation of "n" different things taken "k" at a time, with or without repetition is ${}_k^{n}P=\frac{n!}{(n-k)!}$

In the above question we have to arrange $4$ different books taken all at a time.

So, $n=4$ and $k=4$

Number of ways $={}_4^{4}P=\frac{4!}{(4-4)!}=\frac{4!}{0!}=4!.$