Finding test cases to kill the alive mutants in Mutation testing needs to calculate the Reachability, Infection and Propagation(RIP) conditions and full test specification. In this paper, a formal approach to calculate RIP conditions is proposed. The Dijkestra's weakest precondition predicate transformer (wp(_,_)) is used to calculate infection and propagation conditions. The rc(_) function is defined to calculate the reachability conditions generated by each statement. Four programs and their mutants are examined as running examples and as case studies to show the applicability of the method.