GCF of 7 and 21
GCF of 7 and 21 is the largest possible number that divides 7 and 21 exactly without any remainder. The factors of 7 and 21 are 1, 7 and 1, 3, 7, 21 respectively. There are 3 commonly used methods to find the GCF of 7 and 21  long division, prime factorization, and Euclidean algorithm.
1.  GCF of 7 and 21 
2.  List of Methods 
3.  Solved Examples 
4.  FAQs 
What is GCF of 7 and 21?
Answer: GCF of 7 and 21 is 7.
Explanation:
The GCF of two nonzero integers, x(7) and y(21), is the greatest positive integer m(7) that divides both x(7) and y(21) without any remainder.
Methods to Find GCF of 7 and 21
The methods to find the GCF of 7 and 21 are explained below.
 Using Euclid's Algorithm
 Listing Common Factors
 Long Division Method
GCF of 7 and 21 by Euclidean Algorithm
As per the Euclidean Algorithm, GCF(X, Y) = GCF(Y, X mod Y)
where X > Y and mod is the modulo operator.
Here X = 21 and Y = 7
 GCF(21, 7) = GCF(7, 21 mod 7) = GCF(7, 0)
 GCF(7, 0) = 7 (∵ GCF(X, 0) = X, where X ≠ 0)
Therefore, the value of GCF of 7 and 21 is 7.
GCF of 7 and 21 by Listing Common Factors
 Factors of 7: 1, 7
 Factors of 21: 1, 3, 7, 21
There are 2 common factors of 7 and 21, that are 1 and 7. Therefore, the greatest common factor of 7 and 21 is 7.
GCF of 7 and 21 by Long Division
GCF of 7 and 21 is the divisor that we get when the remainder becomes 0 after doing long division repeatedly.
 Step 1: Divide 21 (larger number) by 7 (smaller number).
 Step 2: Since the remainder = 0, the divisor (7) is the GCF of 7 and 21.
The corresponding divisor (7) is the GCF of 7 and 21.
☛ Also Check:
 GCF of 6 and 24 = 6
 GCF of 25 and 90 = 5
 GCF of 2 and 5 = 1
 GCF of 24 and 60 = 12
 GCF of 12 and 14 = 2
 GCF of 28 and 49 = 7
 GCF of 68 and 102 = 34
GCF of 7 and 21 Examples

Example 1: The product of two numbers is 147. If their GCF is 7, what is their LCM?
Solution:
Given: GCF = 7 and product of numbers = 147
∵ LCM × GCF = product of numbers
⇒ LCM = Product/GCF = 147/7
Therefore, the LCM is 21. 
Example 2: For two numbers, GCF = 7 and LCM = 21. If one number is 7, find the other number.
Solution:
Given: GCF (x, 7) = 7 and LCM (x, 7) = 21
∵ GCF × LCM = 7 × (x)
⇒ x = (GCF × LCM)/7
⇒ x = (7 × 21)/7
⇒ x = 21
Therefore, the other number is 21. 
Example 3: Find the greatest number that divides 7 and 21 exactly.
Solution:
The greatest number that divides 7 and 21 exactly is their greatest common factor, i.e. GCF of 7 and 21.
⇒ Factors of 7 and 21: Factors of 7 = 1, 7
 Factors of 21 = 1, 3, 7, 21
Therefore, the GCF of 7 and 21 is 7.
FAQs on GCF of 7 and 21
What is the GCF of 7 and 21?
The GCF of 7 and 21 is 7. To calculate the greatest common factor of 7 and 21, we need to factor each number (factors of 7 = 1, 7; factors of 21 = 1, 3, 7, 21) and choose the greatest factor that exactly divides both 7 and 21, i.e., 7.
If the GCF of 21 and 7 is 7, Find its LCM.
GCF(21, 7) × LCM(21, 7) = 21 × 7
Since the GCF of 21 and 7 = 7
⇒ 7 × LCM(21, 7) = 147
Therefore, LCM = 21
☛ GCF Calculator
What are the Methods to Find GCF of 7 and 21?
There are three commonly used methods to find the GCF of 7 and 21.
 By Prime Factorization
 By Listing Common Factors
 By Long Division
How to Find the GCF of 7 and 21 by Long Division Method?
To find the GCF of 7, 21 using long division method, 21 is divided by 7. The corresponding divisor (7) when remainder equals 0 is taken as GCF.
What is the Relation Between LCM and GCF of 7, 21?
The following equation can be used to express the relation between Least Common Multiple and GCF of 7 and 21, i.e. GCF × LCM = 7 × 21.
How to Find the GCF of 7 and 21 by Prime Factorization?
To find the GCF of 7 and 21, we will find the prime factorization of the given numbers, i.e. 7 = 7; 21 = 3 × 7.
⇒ Since 7 is the only common prime factor of 7 and 21. Hence, GCF (7, 21) = 7.
☛ Prime Number
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