Statistics

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when determining the median, we need to consider two cases.

- When n, the number of values, is odd, then the median is the middle value once the numbers are arranged in ascending order. - When there is an even number of values, the median is the average of the two middle values.

Set A contains 120 terms with an average of 8.2. Set B contains 240 terms with an average of 10.6. If Set A and B are combined what is the resulting average?

8.2 + 10.6= 18.8/2= 9.4

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.

The mean of twenty-five consecutive positive integers numbers is what percent of the total?

The average is always a fraction of the total that corresponds to the number of numbers. Meaning, to find the mean, we always divide the total by the number of numbers you are adding up. If you have four numbers, then the mean will be ¼ of the total. If you five numbers, the mean will be 1/5 of the total. In the problem above we have 25 numbers (it doesn't really matter that they are consecutive). The mean will be 1/25 of the total, or (A) 4%.

mean; 30.5 , Median= 6 and Mode= 6

The mean is 30.5, the median is 6, and the mode is 6. So in this case, the mean is quite different from the median and mode. The reason for this is that the 300 here changed the mean calculations significantly. So as you can see, the mean of a set of numbers is greatly influenced by numbers that deviate considerably from the other numbers. Also, notice that the 300 here had no effect on the median and the mode

average= mean= arithmetic mean

To find the average of n numbers, we calculate the sum of the n numbers, and then divide this by n

20 students from Mrs. Peterson's English class take her final, and score an average of 75 points. Mr. Chang, who is known for administering far easier tests, has 30 students, and they score an average of 95 points. If we combine the tests from the two classes what is the average score?

[30(95) + 20(75)]/(30+20). With a calculator handy on the GRE, I'd actually recommend this method

nokte testi for median

odd number= for example 7 numbers 7/2= 3.5 and then round up so the 4th is the median even number = for example 8 numbers, 8/2=4 so the 4th and 5th /2

Now, this formula is very useful for solving many GRE questions related to average, so be sure to consider using it when you encounter a question involving average. what is that?

sum of n numbers= (mean)(n) This formula tells us that the sum of the n numbers in a set will be equal to the mean of those numbers times n.

Mode

A third way to describe a set of numbers is to use the mode. The mode of a set of numbers is defined as the number that occurs most frequently in the set.

range

Another concept is range. Above the range of my push-ups friends would be the difference between the greatest and the smallest: John: 10 Ray: 15 Cyrus: 22 Sue: 33

median

Another way to describe a set of numbers is to use the median. The median is defined as the middle most value of a set when the numbers in that set are arranged in ASCENDING order. If it's not ascending, you have re-arrange in this way.

the mean will always equal the median if

In this lesson, we learned that if a set consists of evenly spaced numbers, then the mean and median of that set are equal, and we learned that the converse of this property is not necessarily true.


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