GCF for 21 and 28
"Greatest Common Factor" Calculator
What is the Greatest common Divisor of 21 and 28?
Answer: GCF of 21 and 28 is 7
(Seven)
Finding GCF for 21 and 28 using all factors (divisors) listing
The first method to find GCF for numbers 21 and 28 is to list all factors for both numbers and pick the highest common one:
All factors of 21: 1, 3, 7, 21
All factors of 28: 1, 2, 4, 7, 14, 28
So the Greatest Common Factor for 21 and 28 is 7
Finding GCF for 21 and 28 by Prime Factorization
The second method to find GCF for numbers 21 and 28 is to list all Prime Factors for both numbers and multiply the common ones:
All Prime Factors of 21: 3, 7
All Prime Factors of 28: 2, 2, 7
As we can see there is only one Prime Factor common to both numbers. It is 7
So 7 is the Greatest Common Factor of 21 and 28
Related Calculations
See Also
- Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
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About "Greatest Common Factor" Calculator
This calculator will help you find the greatest common factor (GCF) of two numbers. For example, it can help you find out what is the Greatest common Divisor of 21 and 28? (The answer is: 7). Select the first number (e.g. '21') and the second number (e.g. '28'). After that hit the 'Calculate' button.
Greatest Common Factor (GCF) also known as the Greatest Common Divisor (GCD) or Highest Common Factor (HCF) - it is the largest positive integer that divides each of the integers with zero remainder