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Determine the prime factors for both numbers
18 = 2 x 3 x 3
21 = 3 x 7
As 3 is the only factor common to both numbers then 3 is the Lowest Common Factor and the Highest Common Factor.
NOTE : In general questions are asked for the HighestCommon Factor and/or the Least (or Lowest Common Multiple.
In case the LCM is required , then this is the product of the highest power of each prime factor. Hence, LCM = 2 x 32 x 7 = 2 x 9 x 7 = 126
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Lowest common multiple of 18 and 21?
The Least Common Multiple of 18 and 21 is 126.
Which number goes into 21 and 18?
The highest common factor of 21 and 18 is 3
What is the highest common factor of 18 and 21?
Factors of 18 are 3,3,& 2. Factors of 21 are 3 & 7 One lot of '3' is common to both so '3' is the HCF.
Three 3 is a common factor of 21 and 22?
Three (3) is a common factor of 21 and 22.
What is the greatest common factor for 21 and 36?
The factors of 21 are 1, 3, 7, and 21. The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, and 36. The factors they have in common are 1 and 3, the largest of which is 3, so 3 is the greatest common factor. Or, you can calculate the greatest common factor by looking at the prime factors. The prime factors of 21 are 3 and 7. The prime factors of 36 are 2, 2, 3, and 3. The prime factors they have in common are a single 3, so 3 is the greatest common factor.
