Hey!
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A composite number is a number that has more than one factor other than 1 and itself.
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Factors of 11: 1 and 11
Factors of 21: 1, 3 and 7, 21
Factors of 31: 1 and 31
Factors of 41: 1 and 41
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So buy seeing all the factors of each number the only one that is composites is 21.
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Answer:
21
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Hope This Helped! Good Luck!