100 LearnersLast updated on August 5th, 2025
GCF of 72 and 90
The GCF is the largest number that can divide two or more numbers without leaving any remainder. GCF is used to share the items equally, to group or arrange items and schedule events. In this topic, we will learn about the GCF of 72 and 90.
What is the GCF of 72 and 90?
The greatest common factor of 72 and 90 is 18. The largest divisor of two or more numbers is called the GCF of the number. 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 72 and 90?
To find the GCF of 72 and 90, a few methods are described below:
- Listing Factors
- Prime Factorization
- Long Division Method / by Euclidean Algorithm
GCF of 72 and 90 by Using Listing of Factors
Steps to find the GCF of 72 and 90 using the listing of factors:
Step 1: Firstly, list the factors of each number.
Factors of 72 = 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72.
Factors of 90 = 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90.
Step 2: Now, identify the common factors of them. Common factors of 72 and 90: 1, 2, 3, 6, 9, 18.
Step 3: Choose the largest factor. The largest factor that both numbers have is 18. The GCF of 72 and 90 is 18.
GCF of 72 and 90 Using Prime Factorization
To find the GCF of 72 and 90 using the Prime Factorization Method, follow these steps:
Step 1: Find the prime factors of each number
Prime Factors of 72: 72 = 2 x 2 x 2 x 3 x 3 = 23 x 32
Prime Factors of 90: 90 = 2 x 3 x 3 x 5 = 2 x 32 x 5
Step 2: Now, identify the common prime factors.
The common prime factors are: 2 x 3 x 3 = 2 x 32
Step 3: Multiply the common prime factors 2 x 32 = 2 x 9 = 18.
The Greatest Common Factor of 72 and 90 is 18.
GCF of 72 and 90 Using Division Method or Euclidean Algorithm Method
Find the GCF of 72 and 90 using the division method or Euclidean Algorithm Method. Follow these steps:
Step 1: First, divide the larger number by the smaller number
Here, divide 90 by 72 90 ÷ 72 = 1 (quotient), The remainder is calculated as 90 − (72×1) = 18
The remainder is 18, not zero, so continue the process
Step 2: Now divide the previous divisor (72) by the previous remainder (18)
Divide 72 by 18 72 ÷ 18 = 4 (quotient), remainder = 72 − (18×4) = 0
The remainder is zero, the divisor will become the GCF.
The GCF of 72 and 90 is 18.
Common Mistakes and How to Avoid Them in GCF of 72 and 90
Finding GCF of 72 and 90 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 72, students may mention 11 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 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 72 and 90 Examples
Problem 1
A baker has 72 chocolate muffins and 90 vanilla muffins. He wants to pack them into boxes with the largest number of muffins in each box, ensuring each box has the same number of muffins. How many muffins will be in each box?
We should find the GCF of 72 and 90 GCF of 72 and 90
2 x 32 = 2 x 9 = 18.
There are 18 muffins in each box
72 ÷ 18 = 4
90 ÷ 18 = 5
There will be 18 muffins per box, and each box will contain 4 chocolate muffins and 5 vanilla muffins.
Explanation
As the GCF of 72 and 90 is 18, the baker can make 18 muffins per box.
Now divide 72 and 90 by 18.
Each box will contain 4 chocolate muffins and 5 vanilla muffins.
Problem 2
A gardener has 72 tulips and 90 roses. She wants to plant them in rows with the same number of flowers in each row, using the largest possible number of flowers per row. How many flowers will be in each row?
GCF of 72 and 90
2 x 32 = 2 x 9 = 18.
So each row will have 18 flowers.
Explanation
There are 72 tulips and 90 roses.
To find the total number of flowers in each row, we should find the GCF of 72 and 90.
There will be 18 flowers in each row.
Problem 3
A tailor has 72 meters of silk and 90 meters of cotton. She wants to cut both fabrics 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 72 and 90.
The GCF of 72 and 90 2 x 32 = 2 x 9 = 18.
The fabric is 18 meters long.
Explanation
For calculating the longest length of the fabric first we need to calculate the GCF of 72 and 90 which is 18.
The length of each piece of fabric will be 18 meters.
Problem 4
A carpenter has two wooden planks, one 72 cm long and the other 90 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 72 and 90
2 x 32 = 2 x 9 = 18.
The longest length of each piece is 18 cm.
Explanation
To find the longest length of each piece of the two wooden planks, 72 cm and 90 cm, respectively.
We have to find the GCF of 72 and 90, which is 18 cm.
The longest length of each piece is 18 cm.
Problem 5
If the GCF of 72 and ‘a’ is 18, and the LCM is 360. Find ‘a’.
The value of ‘a’ is 90.
Explanation
GCF x LCM = product of the numbers
18 × 360 = 72 × a
6480 = 72a
a = 6480 ÷ 72 = 90
FAQs on the Greatest Common Factor of 72 and 90
1.What is the LCM of 72 and 90?
2.Is 90 divisible by 5?
3.What will be the GCF of any two prime numbers?
4.What is the prime factorization of 72?
5.Are 72 and 90 prime numbers?
6.How can children in United Kingdom use numbers in everyday life to understand GCF of 72 and 90?
7.What are some fun ways kids in United Kingdom can practice GCF of 72 and 90 with numbers?
8.What role do numbers and GCF of 72 and 90 play in helping children in United Kingdom develop problem-solving skills?
9.How can families in United Kingdom create number-rich environments to improve GCF of 72 and 90 skills?
Important Glossaries for GCF of 72 and 90
- Factors: Factors are numbers that divide the target number completely. For example, the factors of 18 are 1, 2, 3, 6, 9, and 18.
- Multiple: Multiples are the products we get by multiplying a given number by another. For example, the multiples of 5 are 5, 10, 15, 20, 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 30 are 2, 3, and 5.
- Remainder: The value left after division when the number cannot be divided evenly. For example, when 13 is divided by 5, the remainder is 3 and the quotient is 2.
- LCM: The smallest common multiple of two or more numbers is termed LCM. For example, the LCM of 72 and 90 is 360.
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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.
