The greatest common divisor (GCD), also called the greatest common factor (GCF) or highest common factor (HCF), is the largest positive integer that divides two or more numbers without a remainder. For example, the GCD of 8 and 12 is 4, written as GCD(8, 12) = 4. To understand GCD, we must first understand factors. A factor of a number divides it evenly without leaving a remainder. For instance, the factors of 12 are 1, 2, 3, 4, 6, and 12. Common factors between numbers are those that divide all given numbers. For example, the common factors of 16 and 24 are 1, 2, 4, and 8, with 8 being the greatest common divisor.
There are several methods to find the GCD of numbers. The listing method involves writing out all factors of each number and identifying the largest common factor. The prime factorization method breaks down numbers into their prime factors and multiplies the common prime factors. The long division method uses successive divisions until the remainder becomes zero, with the last divisor being the GCD. The repeated division method divides numbers by their smallest common prime factor until no common factors remain. Finally, Euclid's division algorithm expresses the larger number in terms of the smaller one and continues the process until the remainder becomes zero, with the last divisor being the GCD.
Examples of Finding Greatest Common Divisor (GCD) Example 1: Finding the GCD Using the Listing Method Problem:Find the GCD of 24 and 30 using the listing method.
Step-by-step solution:Step 1, Write down all the factors of each number:
Factors of 24 = 1, 2, 3, 4, 6, 8, 12, 24 Factors of 30 = 1, 2, 3, 5, 6, 10, 15, 30Step 2, Identify the common factors between the two numbers. Looking at both lists, the common factors are 1, 2, 3, and 6.
Step 3, Select the largest number from the common factors. In this case, 6 is the largest common factor.
Therefore, GCD(24, 30) = 6. Example 2: Finding the GCD Using the Prime Factorization Method Problem:Find the greatest common divisor of 24 and 36.
Step-by-step solution:Step 1, Break down each number into its prime factors:
For 24:
24 ÷ 2 = 12 12 ÷ 2 = 6 6 ÷ 2 = 3 3 ÷ 3 = 1 So, 24 = 2 × 2 × 2 × 3 = 23×32^3 \times 323×3For 36:
36 ÷ 2 = 18 18 ÷ 2 = 9 9 ÷ 3 = 3 3 ÷ 3 = 1 So, 36 = 2 × 2 × 3 × 3 = 22×322^2 \times 3^222×32Step 2, Identify the common prime factors. Look for prime numbers that appear in both factorizations, taking the minimum power they appear.
Common factors: 2 appears twice in both numbers, and 3 appears once in 24 and twice in 36. So the common factors are 222^222 and 313^131.Step 3, Multiply the common prime factors to find the GCD:
GCD(24, 36) = 22×312^2 \times 3^122×31 = 4 × 3 = 12 Therefore, the greatest common divisor of 24 and 36 is 12. Example 3: Finding the GCD Using the LCM Method Problem:If the LCM(15, 70) = 210, find the greatest common divisor of 15 and 70.
Step-by-step solution:Step 1, Recall the relationship between LCM and GCD:
GCD(a, b) = (a × b) ÷ LCM(a, b)Step 2, Substitute the values into the formula:
a = 15 b = 70 LCM(15, 70) = 210Step 3, Multiply the two numbers:
15 × 70 = 1,050Step 4, Divide this product by the LCM:
GCD(15, 70) = 1,050 ÷ 210 = 5 Therefore, the greatest common divisor of 15 and 70 is 5. Comments(6)MMsTraveler25September 17, 2025I’ve used the Greatest Common Divisor GCD definition and examples from this page to help my kids with their math homework. The step-by-step explanations made it so easy for them to understand!NNatureLover25September 10, 2025I’ve been helping my son with math, and this page was a lifesaver! The step-by-step examples for finding the GCD made it so much easier for him to understand. Thanks for breaking it down so clearly!NNatureLover85August 27, 2025I used the GCD explanation to help my kid with their math homework, and it made things so much easier! The examples are super clear, and the step-by-step methods really helped them understand.MHMrs. HarperAugust 20, 2025I’ve used the GCD examples here to help my kids with their math homework, and it’s a game-changer! The step-by-step explanations made it so easy for them to grasp the concept.MMathMom42August 6, 2025I’ve been using this definition to help my kids with their math homework—it’s so clear and the examples make it easy for them to understand. Highly recommend it!svg]:px-3 dk:w-auto h-10 dk:h-14 rounded-lg dk:rounded-[15px] px-5 dk:px-7.5 text-sm dk:text-xl text-[#3467FF] bg-white hover:bg-white">Load MoreExplore More TermsSmallerBisectCircumference of The EarthCongruentMultiplying Mixed NumbersTally MarkView All Math TermsRecommended Interactive LessonsOne-Step Word Problems: Division3Math3.OA.D.8Identify Patterns in the Multiplication Table3Math3.OA.D.9Understand the Commutative Property of Multiplication3Math3.OA.B.5Use Arrays to Understand the Associative Property3Math3.OA.B.5Word Problems: Addition within 1,0003Math3.NBT.A.2Word Problems: Addition, Subtraction and Multiplication3Math3.OA.D.8View All Interactive LessonsRecommended VideosMeasure Lengths Using Like Objects1Math1.MD.A.2Divisibility Rules4Math4.OA.B.4Classify Triangles by Angles4Math4.G.A.2Multiply to Find The Volume of Rectangular Prism5Math5.MD.C.5a, 5.MD.C.5bPrime Factorization6Math6.NS.B.4Use Equations to Solve Word Problems6Math6.EE.B.7View All VideosRecommended WorksheetsDescribe Positions Using Next to and BesideKMathK.G.A.1Order Numbers to 10KMathK.CC.A.2Count by Ones and Tens1Math1.NBT.A.1Area of Composite Figures3Math3.MD.C.7.dUnderstand and Write Equivalent Expressions6Math6.EE.A.3, 6.EE.A.4Powers And Exponents6Math6.EE.A.1View All WorksheetsRecommended Coloring PagesChristmas teddy bear sitting with a large bow around its neckPre-K – KAll SubjectsA bowl of rice pudding with a spoon and a napkin beside it1 – 2All SubjectsCommuter bike with a small dog in the basket1 – 2All SubjectsNumber 13 with wands with a detailed background of a castle and magical creatures.3 – 4All SubjectsHippopotamus in a zoo enclosure with visitors watching5 – 6All SubjectsTwo piglets walking through a detailed farmyard with plants, tools, and a barn in the background5 – 6All SubjectsView All Coloring PagesRecommended BlogsABCya Sound Burst: A Teacher's Guide to Interactive Phonics LearningNovember 16, 2025Science Games Transform Middle School Learning: A Path to Better Engagement and UnderstandingNovember 16, 2025Fireboy and Watergirl Online Multiplayer: Fun Math Games Kids Can Play TogetherNovember 15, 2025Can You Make Your Dog Sit in Bloxd.io? A Parent's Guide to Gaming and Real-World LearningNovember 15, 2025Runaway Toad: The Perfect Math Game for Your ClassroomNovember 15, 2025Suika Watermelon Game: 5 Math Strategies for K-6 ClassroomsNovember 14, 2025View All Blog PostsQUICK LINKSAbout UsPrivacy PolicyTerms of ServiceTOOLSHomework HelperGuide DesignerPodcast MakerPlan BuilderRESOURCESMath GlossaryEnglish GlossaryEnglish Language ArtsMathematicsScienceBook InsightsFun with WordsBlog© 2025 EDU.COM. All rights reserved.智能索引记录
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