Ken is able to perform mathematical operations only if he can use real objects and familiar examples in counting or working out his answers. ken is in which of piaget's stage.

Ken is in Piaget's concrete operational stage.

Explanation:

According to Piaget, the concrete operational stage begins when children are around 7 years old. In this stage, logical thought begins to develop and children become more logical, nonetheless, their thinking is still very concrete. Their problem solving abilities are still narrowed to concrete and specific things, like Ken, who is able to perform mathematical operations if he can use real objects or familiar examples.

The concrete operational stage is followed by the formal operational stage.

b) the planets year length would be longer

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answer; did not understand that the act was wrong because she/he was suffering from a mental illness;