Question 1059577: 117. On a shelf there are 4 books on Economics, 3 books on
Management and 4 books on Statistics. In how many
different ways can the books be arranged so that the
books on Economics are kept together?
1) 967680 2) 20960 3) 5040
4) 40320 5) None of these
Answer by addingup(3677)   (Show Source):
You can put this solution on YOUR website! You have 3 subjects, so 3!
Then you have Economics, there are 4 ways to do this. But since they have to stay together but not in any particular order, consider the 4 books as 1 "lump" or 1 big book. So, we have 1+3+4 = 8 books and we can arrange them in 8! ways (See? by calling the Economics books 1 we always keep them together).
So now we have 3!8! = 241,920 ways to arrange the books, always keeping the Economics books together.
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