GRE数学重要知识点汇总

    Set

    A set is a collection of objects or things. Each object in a set a member or element of that set.Size of a set is the number of members in the set.

    Example:

    The set of even numbers between 2 and 10 is of size 5:{2,4,6,8,10}.

    The set of primes between 2 and 10 is of size 4:{2,3,5,7}.

    Remember:

    Each member of set A belongs to A or is in the set A.

    A set can not have repeating member:{1,3,1,2}is not a set.

    Rearranging the order of the members does not change the set:{1,2,3}is same as{3,2,1}.

    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.

    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.