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2012年新GRE数学考点指导排列

发布时间: 2012-11-02 05:18:23 作者: sxsgeass

  Permutation of Objects

  The number of ways n distinct objects can be ordered is n!.

  Example:

  Number of ways 6 people can from a queue is 6!.

  Number of ways 5 different cars can be parked in 5 parking spaces is 5!.

  Remember: 

  This does not apply if there are identical objects or ordering does not matter.

  Permutation with Selection

  The number of ways n objects drawn from a collection of m distinct objects can be ordered is m!/(m-n)!.

  Example:

  Number of ways a queue of length 3 can be formed from a group of 5 people is 5!/(5-3)!=5!/2!=5*4*3=60.

  Number of possible top ten list for 150 movies is 150!/(150-10)!.

  Remember:

  This does not apply if there are identical objects or ordering does not matter

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