Kata

Consider X as the aleatory variable that count the number of letters in a word. Write a function that, give in input an array of words (strings), calculate the variance of X. Max decimal of the variance : 4.

Some wiki: Variance , Aleatory variable

Example:

Consider "Hello" and "World":

X is { 5 } with P(X = 5) = 1 because the two words have the same length.
So E[X] = 5 x 1 = 5 and the standard formula for variance is E[(X - u)^2] so 1 x (5-5)^2 = 0 or you can calculate with the other formula E[X^2] - E[X]^2 = 5^2 x 1 - 5^2 = 0

Consider "Hi" and "World":

X is { 2, 5 } with P(X = 5) = 1/2 and P(X = 2) = 1/2.
So E[X] = 5 x 1/2 + 2 x 1/2 = 3.5 and the standard formula for variance is E[(X - u)^2] so 1/2 x (2-3.5)^2 + 1/2 x (5 - 3.5)^2 = 2.25 or you can calculate with the other formula E[X^2] - E[X]^2 = (5^2 x 1/2 + 2^2 x 1/2) - 3.5^2 = 2.25