Piaget believed that people resolve the formal operational stage by age 15, but some estimates show that percent of adults are capable of complete formal operational thinking.

The answer is "25%".

The formal operational stage starts at roughly age 12 and keeps going into adulthood. At this time, individuals build up the capacity to consider theoretical ideas. Aptitudes, for example, legitimate idea, deductive thinking, and deliberate arranging likewise rise in this stage.

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Yes all of them are right