Signed Numbers Arithmetic Operation in Multi-Membrane

P - systems are computing models, where certain objects can evolve in parallel into a hierarchical membrane structure. Recent results show that this model is a promising framework for solving NP-complete problems in polynomial time. The present paper considers the possibility to perform operations with signed numbers in a P - system. All four arithmetical operations are implemented in a way which seems to have a lower complexity than when implementing them in usual Computer Architecture.