The work that Yi did to find the greatest common factor of 42 and 63 is shown below.Factors of 42: 1, 2, 3, 6, 7, 14, 21, 42Factors of 63: 1, 7, 9, 63The greatest common factor is 7.What is Yi’s error?

Yi’s list for 63 is missing factors: 3 divides 63, and so do 21. The complete list includes 1, 3, 7, 9, 21, and 63. Since 21 is a factor of both 42 and 63, the greatest common factor is 21, not 7. The error is that Yi did not list all the factors of 63.

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