Final answer:
The final stage in Piaget's theory of cognitive development is the formal operational stage, where individuals can think abstractly and use deductive logic to formulate and test hypotheses.
Step-by-step explanation:
The final stage in Piaget's theory of cognitive development is the formal operational stage. In this stage, individuals can think abstractly and formulate and test hypotheses through deductive logic. Children in the formal operational stage are able to problem solve using abstract thinking, consider alternative solutions, and evaluate them using logical reasoning. This stage occurs from about age 11 to adulthood.