Question 785651: How many ways can 5 different books be arranged if one book cannot be at either ends??
Answer by xinxin(76)   (Show Source):
You can put this solution on YOUR website! Draw 5 slots:
___ ___ ___ ___ ___
Since one book should be in the middle slots, we will get 3 situations:
(1)_4_ _1_ _3_ _2_ _1_
(2)_4_ _3_ _1_ _2_ _1_
(3)_4_ _3_ _2_ _1_ _1_
* The numbers (4,3,2,1) indicate the number of books can be put in the slot.
Th answer is 4*3*2*1*1 + 4*3*1*2*1 + 4*3*2*1*1 = 72
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