mean-median-mode-range-std.txt

Mean -> Sum of all elements divided by number of elements. Arithmetic mean = average.
Median -> middle element after sorting all elements. If there are even number of elements, then get the mean of middle elements.
Mod -> Most repeated element (if there is one).
Range -> biggest element minus smallest element.


Standard deviation (sigma) -> how spread out the numbers are. Square root of variance.
Mean diviation - How far, on average, all values are from the middle. square root of absolute variance.
Variance (mu) -> average of squared differences from mean. That is (element - mean) squared for each element and find the mean of it.

If the numbers are a sample, rather than whole population, divide by N-1 instead of N while calculating variance. (Bessel's correction).


Factorial -> n! -> 1x2x..xn. Number of ways to arrange n objects. Each selection reduces available pool for next selection. ie., no repetition.
Permutation -> nPr = n!/(n-r)!. Ways to arrange r objects from a collection of n objects.
Combination -> nCr = n!/r!(n-r)!. Ways to select r bjects from a collection of n objects without considering order.

If repetition is allowed:
Permutation -> n to the power of r.
Combination -> (r+n-1)!/r!(n-1)!