Probability calculator Formula:
   P(A) = N_A / N_T
   P(B) = N_B / N_T
   P(A∩B) = P(A) × P(B)
   P(A∪B) = P(A) + P(B) - P(A∩B)
   P(A|B) = P(A∩B) / P(B)
   P(B|A) = P(A∩B) / P(A)