How to find the greatest common factor (GCF) of two or more whole numbers in maths? Grade 7 maths questions are presented along with Detailed Solutions and explanations are included.
What is the greatest common factor (GCF) in math?
1  Method that may be used for small numbers Examples: Find greatest common factor of the numbers 12 and 18. 1) List all the factors of 12 which are: 1, 2, 3 , 4, 6, 12 2) List all the factors of 18 which are: 1, 2, 3 , 6, 9, 18 Look for the common factors of 12 and 18: 1, 2, 3, and 6. The greatest of the common factor (GCF) of 12 and 18 is 6. 2  Method that may be used for all numbers including large numbers Examples: Find greatest common factor of the numbers 60 and 90. 1) The prime factorization of 60 is: 60 = 2^{ 2}×3×5 = 2×2×3×5 2) The prime factorization of 90 is: 90 = 2 × 3^{ 2}×5 = 2×3×3×5 Look for the common factors of 60 and 90 in the prime factorization: 2, 3, and 5. The greatest common factor (GCF) of 60 and 90 is 2×3×5 = 30. A Greatest Factor Calculator (GCF) may be used to check your answers.

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