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103 LearnersLast updated on September 10, 2025
GCF of 15 and 51
The GCF is the largest number that can divide two or more numbers without leaving any remainder. GCF is used to share items equally, to group or arrange items, and schedule events. In this topic, we will learn about the GCF of 15 and 51.
What is the GCF of 15 and 51?
The greatest common factor of 15 and 51 is 3. The largest divisor of two or more numbers is called the GCF of the numbers. If two numbers are co-prime, they have no common factors other than 1, so their GCF is 1. The GCF of two numbers cannot be negative because divisors are always positive.
How to find the GCF of 15 and 51?
To find the GCF of 15 and 51, a few methods are described below -
- Listing Factors
- Prime Factorization
- Long Division Method / by Euclidean Algorithm
GCF of 15 and 51 by Using Listing of factors
Steps to find the GCF of 15 and 51 using the listing of factors
Step 1: Firstly, list the factors of each number
Factors of 15 = 1, 3, 5, 15.
Factors of 51 = 1, 3, 17, 51.
Step 2: Now, identify the common factors of them Common factors of 15 and 51: 1, 3.
Step 3: Choose the largest factor The largest factor that both numbers have is 3. The GCF of 15 and 51 is 3.
GCF of 15 and 51 Using Prime Factorization
To find the GCF of 15 and 51 using the Prime Factorization Method, follow these steps:
Step 1: Find the prime factors of each number Prime Factors of 15: 15 = 3 x 5 Prime Factors of 51: 51 = 3 x 17
Step 2: Now, identify the common prime factors The common prime factor is: 3
Step 3: Multiply the common prime factor 3 = 3 The Greatest Common Factor of 15 and 51 is 3.
GCF of 15 and 51 Using Division Method or Euclidean Algorithm Method
Find the GCF of 15 and 51 using the division method or Euclidean Algorithm Method. Follow these steps:
Step 1: First, divide the larger number by the smaller number Here, divide 51 by 15 51 ÷ 15 = 3 (quotient), The remainder is calculated as 51 − (15×3) = 6 The remainder is 6, not zero, so continue the process
Step 2: Now divide the previous divisor (15) by the previous remainder (6) Divide 15 by 6 15 ÷ 6 = 2 (quotient), remainder = 15 − (6×2) = 3 Continue the process
Step 3: Now divide the previous divisor (6) by the previous remainder (3) Divide 6 by 3 6 ÷ 3 = 2 (quotient), remainder = 6 − (3×2) = 0
The remainder is zero, the divisor will become the GCF. The GCF of 15 and 51 is 3.
Common Mistakes and How to Avoid Them in GCF of 15 and 51
Finding GCF of 15 and 51 looks simple, but students often make mistakes while calculating the GCF. Here are some common mistakes to be avoided by the students.
Mistake 1
Listing Incorrect Factors
Students may sometimes list incorrect factors. For example, while listing factors of 15, students may mention 10 which is incorrect. To avoid this, students should carefully divide the number and list the factors correctly.
Mistake 2
Choosing the wrong common factor
Students may sometimes select the smallest common factor instead of the largest one. To avoid this confusion, students should list all the common factors and find the greatest one.
Mistake 3
Forgetting to include 1 as a factor
Sometimes students may forget 1 as a common factor of the numbers. However, it does not affect the GCF, but it tells about the incomplete understanding of the factors. Students should include 1 as a factor.
Mistake 4
Using Multiples instead of factors
Students confuse between factors and multiples. In that confusion, sometimes they may write multiples instead of factors. To avoid this confusion, students should know the definitions of multiples and factors clearly.
Mistake 5
Assuming GCF is always an even number
Students may assume that the GCF of two numbers will always be an even number. But it's not true that a GCF can also be an odd number. To avoid this, students should focus on common factors rather than focusing on even and odd numbers.
Greatest Common Factor of 15 and 51 Examples
Problem 1
A teacher has 15 notebooks and 51 markers. She wants to group them into equal sets, with the largest number of items in each group. How many items will be in each group?
We should find the GCF of 15 and 51 GCF of 15 and 51 3 = 3
There are 3 equal groups 15 ÷ 3 = 5
51 ÷ 3 = 17
There will be 3 groups, and each group gets 5 notebooks and 17 markers.
Explanation
As the GCF of 15 and 51 is 3, the teacher can make 3 groups.
Now divide 15 and 51 by 3. Each group gets 5 notebooks and 17 markers.
Problem 2
A school has 15 red chairs and 51 blue chairs. They want to arrange them in rows with the same number of chairs in each row, using the largest possible number of chairs per row. How many chairs will be in each row?
GCF of 15 and 51 3 = 3 So each row will have 3 chairs.
Explanation
There are 15 red and 51 blue chairs. To find the total number of chairs in each row, we should find the GCF of 15 and 51. There will be 3 chairs in each row.
Problem 3
A tailor has 15 meters of red ribbon and 51 meters of blue ribbon. She wants to cut both ribbons into pieces of equal length, using the longest possible length. What should be the length of each piece?
For calculating the longest equal length, we have to calculate the GCF of 15 and 51 The GCF of 15 and 51 3 = 3 The ribbon is 3 meters long.
Explanation
For calculating the longest length of the ribbon first we need to calculate the GCF of 15 and 51 which is 3. The length of each piece of the ribbon will be 3 meters.
Problem 4
A carpenter has two wooden planks, one 15 cm long and the other 51 cm long. He wants to cut them into the longest possible equal pieces, without any wood left over. What should be the length of each piece?
The carpenter needs the longest piece of wood GCF of 15 and 51 3 = 3
The longest length of each piece is 3 cm.
Explanation
To find the longest length of each piece of the two wooden planks, 15 cm and 51 cm, respectively. We have to find the GCF of 15 and 51, which is 3 cm. The longest length of each piece is 3 cm.
Problem 5
If the GCF of 15 and ‘a’ is 3, and the LCM is 255. Find ‘a’.
The value of ‘a’ is 51.
Explanation
GCF x LCM = product of the numbers
3 × 255 = 15 × a
765 = 15a
a = 765 ÷ 15 = 51
FAQs on the Greatest Common Factor of 15 and 51
1.What is the LCM of 15 and 51?
2.Is 15 divisible by 3?
3.What will be the GCF of any two prime numbers?
4.What is the prime factorization of 51?
5.Are 15 and 51 prime numbers?
Important Glossaries for GCF of 15 and 51
- Factors: Factors are numbers that divide the target number completely. For example, the factors of 15 are 1, 3, 5, and 15.
- Multiple: Multiples are the products we get by multiplying a given number by another. For example, the multiples of 3 are 3, 6, 9, 12, and so on.
- Prime Factors: These are the factors of a number that are prime numbers and divide the given number completely. For example, the prime factors of 51 are 3 and 17.
- Remainder: The value left after division when the number cannot be divided evenly. For example, when 51 is divided by 15, the remainder is 6.
- LCM: The smallest common multiple of two or more numbers is termed LCM. For example, the LCM of 15 and 51 is 255.
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Hiralee Lalitkumar Makwana
About the Author
Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.
Fun Fact
: She loves to read number jokes and games.
