Brain Teasers
How Many Books?
John has 15 books, and poses himself with a challenge: ''If I placed each book side by side, I wonder how many different combinations I could arrange these books in...''.
How many combinations are there?
How many combinations are there?
Answer
130767436800015x14x13x12x11x10x9x8x7x6x5x4x3x2x1=1307674368000
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Comments
I came up with 653,837,184,000 which is 15!/2 (15x14x13x12x11x10x9x8x7x6x5x4x3x2x1)/2. For every combination, there's a reverse combination as well, so I thought you were going for the fact that these "opposite" combinations still put the books in the same order.
realy smart
Cool I got it. Good Teaser smart one
an easy puzzle. I think the anser is fine. Would you notice if your set of encyclopaedias was arranged from Z to A? If so, then backwards is a different order.
By the way, if you chose one book to read and arranged the remaining 14 books on the shelf, how many different orders would be possible then?
By the way, if you chose one book to read and arranged the remaining 14 books on the shelf, how many different orders would be possible then?
These are permutations, not combinations. Combinations are independent of order.
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