Please reason step by step, and put your final answer within \boxed{}.
In a group of 200 people, 80 have an age of more than 40 years, 70 have an age between 30 and 40 years, 30 have an age between 20 and 30 years, and the remaining 20 have an age of less than 20 years. If a person is selected at random from this group, what is the probability that the person's age is between 30 and 40 years?
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