Bunuel wrote:

Official Solution:

Each shelf of a bookcase contained 12 books. If the librarian took out 21 books and rearranged the remaining books so that all shelves but the last one contained 8 books and that last shelf contained 11 books, how many shelves does the bookcase have?

A. 5

B. 6

C. 7

D. 8

E. 9

Say there are total of \(x\) shelves, then: \(12*x=21+8*(x-1)+11\), which gives \(x=6\).

Answer: B

Hi Bunuel,

Thanks for the explanation. However, why do you subtract "1" from 8*(x-1)? Can you please verify?

Thank you so much.

Aram