Class 11

Math

Algebra

Permutations and Combinations

In a library, there are m books of mathematics and n books of natural science. They can be placed on a shelf in $1209600$ ways so that the books of the same subject are not separated.If $m≥n$. then m $=$

- $6$
- $7$
- $8$
- $9$

$m! ×n! ×2!$ $=$ 1209600

By trial and error,

$m! ×n!$ $=$ $7! ×5!$

$m! ×n!$ $=$ $7! ×5!$