Question

There are 4 mathematics books, Junior inter volume 1 & 2, Senior inter volume 1 & 2 among 20 books. They are arranged in a row at random.The probability that all the mathematics books are arranged in that order not necessarily side by side is

• A. $\frac{1}{16}$
• B. $\frac{1}{12}$
• C. $\frac{1}{24}$
• D. $\frac{1}{8}$

Answer 1

Answer: (C)

$\frac{1}{24}$

No. of ways of arranging the books in the above mentioned order = $\frac{20!}{4!}$
Total no. of ways of arranging the books = $20!$
Hence, required probability = $\frac{\frac{20!}{4!}}{20!}=\frac{1}{4!}=\frac{1}{24}$