新GRE数学要点:Permutation
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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