Tom plants a tree that is 1 year old and 5 feet tall. It gains 3 feet per year. How old is it when it is 23 feet tall? Let's think first. Chain of thought:
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It has grown 23 - 5 = 18 feet. So it is 18 / 3 = 6 years older. That means it is 6 + 1 = 7 years old.
Therefore, the answer is 7.
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