Possible Duplicate:
A number of questions “has been” or “have been” asked?
Which one of these sentences is correct?
The number of students are increasing.
or
The number of students is increasing.
Initially I thought the first option wass correct, but later in the solution section of a book, the answer shown is that the sentence is with "is" not "are" is correct.
Am I correct, or is the book correct?