It's called the median point.
The mean or median point.
The median is the 'middle' of a set of numbers. Sort the list and find the middle number. If the set contains an even number of items, then take the middle two numbers and take the average of those two.
addition
Sort the data items into numerical order (ascending is usual, but descending can be used). The median is the number in the middle: If there are an odd number of items in the dataset, then the median is the middle number, which is the (n+1)/2th item (where n is the number of items in the dataset). Otherwise there is an even number of items in the dataset and the median is the mean of the two in the middle. These items are the n/2th and the (n/2 + 1)th items.
When there is an even number of items in the data set the median is the mean average of the middle two. The middle two are the two items themselves, namely 20 and 40, so the median is (20 + 40)/2 = 30.
sorted: 1 2 7 9 11 15 19 20 number of items: 8 middle items: 9 and 11 average of middle items, or median: (9+11)/2 = 10
Whenever there are an even number of items in your data set, the algebraic mean of the 2 middle numbers is the median. So in this case 19.5
dents
If the sample has an odd number of items in it then the median will definitely be in the sample at least once because the median is value of the set of data items whose value(s) are in the middle of the sample when the sample is sorted from smallest to largest. If the sample has an even number of items in it then if the middle items are different the median will be their average, and it will differ from all of the items in the data set. I could continue in this vein but already you can see that the median sometimes occurs in a data set but not always.
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you just play in the halloween room which is called halloween or halloween with a number after it