The number 81 is written as a sum of three natural numbers 81 =
a + b + c (the triple (a,b,c) is ordered; e.g., the decompositions
81 = 1 + 1 + 79 and 81 = 1 + 79 + 1 are different. Also, assume
that all the decompositions have equal probability.) What is the
probability that there exists a triangle with sides a, b, and c?
(PLEASE EXPLAIN THE STEPS AND WHY YOU KNOW TO DO STEPS, THANKS)