Question 1193547: A man possesses 24 books, all different. In how many ways can he arrange 12 of them on a shelf?
Found 3 solutions by Boreal, ikleyn, greenestamps:
Answer by Boreal(15235)   (Show Source):
Answer by ikleyn(52776)  (Show Source):
You can put this solution on YOUR website! .
The answer and the conception in the post by @Boreal is incorrect.
In this problem the order is important, so it asks about PERMUTATIONS, not about combinations.
The answer is this huge number
24*23*22*21*20*19*18*17*16*15*14*13 = 1295295050649600. ANSWER
It is the product of 12 consecutive integer numbers in descending order, starting from the number 24.
Solved.
Answer by greenestamps(13198)  (Show Source):
You can put this solution on YOUR website!
The 24C12 answer from the other tutor is only the number of ways of choosing 12 of the 24 books.
Arranging them on a shelf means order is important, so the answer to the question is 24P12.
ANSWER: 24P12 = (24!)/(12!) = 1,295,295,050,649,600
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