Four different books (A, B, C and D) are to be arranged on a shelf. Books A and B are to be arranged first and second starting from the right of the shelf. The number of different orders in which books C and D may be arranged is
Select:  A) 16!  B) 12!  C) 8!  D) 11!  E) 2!
Solution   Since books A and B are arranged first and second, only books C and D will change order. Therefore it an arrangement problem involving 2 items and the number of different order is given by   2!   Answer 2!
<result>E</result>
Four different books (A, B, C and D) are to be arranged on a shelf. Books A and B are to be arranged first and second starting from the right of the shelf. The number of different orders in which books C and D may be arranged is