In how many ways can 11 books on English and 9 books on French be placed in a row on a shelf so that two books on French may not be together? Answers.
A) 220.
B) 240
C) 260
D) 280
E) 300
We have 11 English and 9 French books, no French books should be adjacent.   Imagine 11 English books in a row and empty slots like below:   *E*E*E*E*E*E*E*E*E*E*E*   Now if 9 French books would be placed in 12 empty slots, all French books will be separated by English books.   So we can "choose" 9 empty slots from 12 available for French books, which is 12C9=220.	220.NS:220.   _________________
<result>A</result>
In how many ways can 11 books on English and 9 books on French be placed in a row on a shelf so that two books on French may not be together?