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Found this post from another gmat forum: https://gmatclub.com/forum/standard-deviation-calculation-of-standard-deviation-sd-69015.html
STANDARD DEVIATION :
Calculation of Standard Deviation (SD):
i) Find the mean of the set of numbers
ii) Find the difference between each of the numbers and the mean
iii) Square the differences and take the mean of the differences (Thanks Ian)
iv) Take the positive square root of this value
It is very unlikely that a GMAT problem will involve calculating the SD of a given series.
1.SD does not change when the same constant is added or subtracted to all the members of the set.
2.A set of numbers with range of zero means that all of the numbers are the same, hence the dispersion of the numbers from its mean is zero. In other words, If the range is 0, then the SD must also be 0, because there is no variance.
3.If Range or SD of a list is 0, then the list will contain all identical elements.
4.You only need to know the difference between values and total number of values to compute SD.
5.If we know all the numbers of the list, there is a definite SD, regardless of what it is, we can compute it and get an answer – this is helpful for DS questions.
6.The SD of any list is not dependent on the average, but on the deviation of the numbers from the average. So just by knowing that two lists having different averages doesn't say anything about their standard deviation - different averages can have the same SD.
7.The sum of the deviations of the elements from the mean must be 0
8.Closer the more values to the MEAN, lower the SD
9.If you multiply all terms by x then SD =x times old SD and the mean = x times old mean
10.For comparing the SD for two sets any information about mean ,median,mode and range are insufficient unless you can determine the individual terms from the given data.
11.If mean = maximum value it means that all values are equal and SD is 0.
12.Variance is the square of the standard deviation
RANGE :
1. Range is the difference between the largest number and smallest number in a set
2. If Range of a list is 0, then the list will contain all identical elements. Or if a set contains all identical elements, then range = 0
3. If a set contains only one item, then range = 0
MODE :
Mode is the most frequently recurring number/numbers among the given set of numbers. It can be more than one
MEAN AND MEDIAN:
1. Arithmetic Mean (Average) = total of quantities / number of quantities
2. The median is the "middle" number in a group (when arranged in ascending or descending order) consisting of an odd number of numbers, and the average of the two middle numbers if there are an even number of numbers
3. For a set of consecutive integers, the median is the the average of the first and the last integer
4. For a given set of consecutive even/odd (or evenly spread) numbers mean = median
5. For a given set of consecutive integers median = mean
http://www.integratedlearning.net/gmat/sample.asp
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发表于 2018-9-9 05:53:42
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