NOTICE THAT THE STANDARD DEVIATION DEPENDS ON EVERY DATA VALUE, ALTHOUGH IT DEPENDS MOST ON VALUES THAT ARE FARTHEST FROM THE MEAN. THIS IS WHY A DISTRIBUTION WITH DATA GROUPED CLOSELY AROUND THE MEAN WILL HAVE A SMALLER STANDARD DEVIATION THAN DATA SPREAD FAR FROM THE MEAN.
6.排列与组合
THERE ARE SOME USEFUL METHODS FOR COUNTING OBJECTS AND SETS OF OBJECTS WITHOUT ACTUALLY LISTING THE ELEMENTS TO BE COUNTED. THE FOLLOWING PRINCIPLE OF MULTIPLICATION IS FUNDAMENTAL TO THESE METHODS.
IF A FIRST OBJECT MAY BE CHOSEN IN M WAYS AND A SECOND OBJECT MAY BE CHOSEN IN N WAYS, THEN THERE ARE MN WAYS OF CHOOSING BOTH OBJECTS.
AS AN EXAMPLE, SUPPOSE THE OBJECTS ARE ITEMS ON A MENU. IF A MEAL CONSISTS OF ONE ENTREE AND ONE DESSERT AND THERE ARE 5 ENTREES AND 3 DESSERTS ON THE MENU, THEN 53 = 15 DIFFERENT MEALS CAN BE ORDERED FROM THE MENU. AS ANOTHER EXAMPLE, EACH TIME A COIN IS FLIPPED, THERE ARE TWO POSSIBLE OUTCOMES, HEADS AND TAILS. IF AN EXPERIMENT CONSISTS OF 8 CONSECUTIVE COIN FLIPS, THE EXPERIMENT HAS 28 POSSIBLE OUTCOMES,SWHERESEACH OF THESE OUTCOMES IS A LIST OF HEADS AND TAILS IN SOME ORDER.
阶乘:FACTORIAL NOTATION
假如一个大于1的整数N,计算N的阶乘被表示为N!,被定义为从1至N所有整数的乘积,
例如:4! = 4321= 24
注意:0! = 1! = 1
排列:PERMUTATIONS
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