In watching two children, wiley, who is in the concrete operational stage, and abby, who is in the formal operational stage, solve piaget's pendulum problem, what difference would be evident?

The evident difference would be that Abby will systematically test alternative hypotheses. The formal operational stage starts at around age twelve and endures into adulthood. As teenagers enter this stage, they pick up the capacity to think in a unique way by manipulate thoughts in their mind, with no reliance on concrete manipulation.