Peanuts by Charles Schulz for May 07, 1974
May 06, 1974
May 08, 1974
Transcript:
Peppermint Patty sits at her desk in school and reads a book. She reads, "A library shelf contains seven books."<BR><BR> Peppermint Patty continues to read, "Three books are math books and four books are science books . . ."<BR><BR> Peppermint Patty reads, "Problem: In how many ways may the books be arranged on the shelf so that all the math books will be together?"<BR><BR> Peppermint Patty shouts, "Defense! Defense!"<BR><BR>
There are three math books, so there are 3! = 6 ways of arranging them. There are four science books, so there are 4! = 24 ways of arranging them. For each way of arranging the science books there are three ways of putting the math books between them, and it is also possible to put the math books before them and after them, so there are five total ways. Thus the number of ways to arrange the books so that the math books are always together is 24 × 5 × 6 = 720.