新GRE数学要点:Combinations
Number of ways we can select n objects from a group of m distinct objects is m!/(n!*(m-n)!). Example:Number of possible ways to pick 4 oscar nominations from a list of 50 movies is 50!/(4!*(50-4)!)=50!/(4!*46!)=50*49*48*47/24=230300
Remember:
This does not apply if there are identical objects.
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