Four books, one each in Chemistry, Physics, Biology and Mathematics, are to be arranged in a shelf. In how many ways can this be done?
Given: the total number of books = 4
To find: Number of ways in which these 4 books can be arranged in a shelf
Formula used:
Number of arrangements of n things taken all at a time = P(n, n)
∴ The total number of ways
= the number of arrangements of 4 things taken all at a time
= P(4, 4)
{∵ 0! = 1}
= 4 × 3 × 2 × 1
= 24
Hence, Number of ways in which these 4 books can be arranged in a shelf are 24
18