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1st March 2016, 01:56 PM
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Join Date: May 2012
Re: GRE Statistics

Some essential concepts to statistics on the Graduate Record Examination (GRE) Math section are as follows:

Mean

The mean is another way of saying average.
To find the average add up the number of elements in the set and divide by the number of elements.

For instance, let’s say I am counting the average number of push-ups my friends can do:

John: 10

Ray: 15

Cyrus: 22

Sue: 33

I find the total: 10+15+22+33=80. I then divide by the number of elements. In this case, I have four friends. 80/4=20, which is the average number.

Another concept is range. Above the range of my push-ups friends would be the difference between the greatest and the smallest: [pmath]33–10=23

Median


The median is the middle number in a list of numbers arranged in ascending order.

For instance, in the list 3, 4, 5, 8, 12, the number 5 is in the middle. Hence it is the median.

A little confusion arises when you have an even set of numbers. 3, 4, 4, 7, 9, 10. In this case 4 and 7, the innermost numbers, cannot both be medians. So we end up taking their average: (4+7)/2 = 5.5.

Mode

Set A: {2, 2, 2, 4, 5.5, 7, 7}

The number that shows up most in a list of numbers is the mode. Because the number two shows up the most frequently it is known as the mode.
A list can have more than one mode, so if we were to add another 7 to the list above, 2 and 7 would both be the mode.
However, if each number shows up only once, then we say that a set either has no mode or that every number in the set is a mode (for the GRE don’t really worry about this last part—I just want to make sure I dot my mathematical “i”s).

Standard Deviation

Set A: 3, 4, 5, 6, 7

Set B: 2, 3, 5, 7, 8

Both sets have the same average.

Notice how the spread in Set B is greater than that in Set A. Or, put another way, the numbers in Set A are clumped more closely together.

The closer the spread (or the “clumpier”) the numbers, the lower the standard deviation

The standard deviation for Set A is approximately 1.4 and that for Set B is approximately 2.3.


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