Add Maths IGCSE

Jess wants to arrange 9 different books on a shelf. There are 4 mathematics book, 3 physics books and 2 chemistry books. Find the number of different possible arrangements of the books if all the mathematics books are kept together and all he physics books are kept together.

Reply 1

kubes_04

13

Since all the maths books are the same, count them as one block, same with all the physics books. Then you get 2 different chemistry books that don't need to be kept together so that gives you 4 different "items". So the number of possibilities is 4! (4 factorial --> 4x3x2x1 = 24 different ways).
I think that's right.

Reply 2

Bigboy696942069

1

4! number of ways to arrange the different groups of books. Taking math as one group, physics as another and the 2 chemistry as separate groups(as they are not together). Then 4! number of ways to arrange within mathematics, 3! in physics and 2! in chemistry. We can then multiply them together to get a final answer of 6912

Reply 3

mqb2766

21

Original post by Bigboy696942069

4! number of ways to arrange the different groups of books. Taking math as one group, physics as another and the 2 chemistry as separate groups(as they are not together). Then 4! number of ways to arrange within mathematics, 3! in physics and 2! in chemistry. We can then multiply them together to get a final answer of 6912

The thread is a couple of years old and I guess the OP has moved past thiis.
While you've got closer (logically) to the answer than #2, for some reason youve double counted chemistry.

(edited 2 years ago)

Add Maths IGCSE

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