In the famous paper of Kurt Gödel he proved that number theory, containing axioms for addition and multiplication is incomplete. But what about simpler theories? Are they complete? The answer is yes. The theories of addition and multiplication are both complete, but the argument that they are decidable is far from trivial. In the following essay we shall present the weak fragments of number theory and outline the proofs why they provide an algorithm answering yes or no on questions about truth.