Complementary cumulative distribution function as the name
suggest complements cumulative distribution function (CDF). Cumulative
Distributive Function (CDF) is used to find the probability of a variable
taking a value less than or equal to x for any given function and one of the
properties of CDF is that it goes to 1 as x tends to infinity. So, at any given
point of time if we sum CDF and CCDF, we will get the resulting number to be 1.

CDF is used to find the probability of a variable taking a
value less than or equal to x, CCDF is used to find the probability of a
variable taking a value greater than x. In simple terms, it is used to
understand how often a random variable is above a particular level. In
actuarial science, the complement of the CDF is called the survival function.

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