In this article, you will certainly learn just how to calculation the Greatest common Factor (GCF) and also Least typical Multiple (LCM) the integers. These an abilities are beneficial in a variety of different situations. Let’s watch what they room all about!

Suppose your mom has actually two rectangular cakes for a party, one vanilla and also one strawberry, both the same thickness. The vanilla flavored cake has actually an area that 12 square inches, while the strawberry flavored cake has an area that 20 square inches. Your mom wants to division both cakes into pieces such that all pieces room of equal size and both cakes are evenly separated with no leftover smaller sized pieces.

You are watching: Difference between greatest common factor and least common multiple


“No problem,” your mom says, “I’ll just reduced the cakes right into 4-square-inch pieces. That way, everyone will have actually a same-sized piece.”

How in the world did she understand that?

More GCF and also LCM Help

The Greatest common Factor

Before we check out the cake situation, let’s remember what factors are. Factors are number that, when multiplied, produce one more number. Usually, we talk around factors in pairs. 1 and 8 are components of 8 due to the fact that 1×8=8. The number 4 and also 2 are additionally factors that 8, due to the fact that 4×2=8.

Numbers have a distinct prime factorization. Recall the prime numbers, prefer 2, 3, and 5, deserve to only be divided by themselves and 1. We can keep dividing the components of any type of number into its prime number components. So, any number is written of a unique collection of element numbers multiply together. Take it a look at these factor trees and what they call us:

Factorizations the 18


The number 18 is originally factored two various ways: 3 and also 6 and additionally 2 and 9. We have the right to see the prime factorization is the same, regardless of our very first factor pair.

2 x 3 x 3 = 18. The purple circles match in both trees.

What go this need to do with the 2 cakes?

Mathematically, your mom calculated the Greatest common Factor (GCF) in between 12 and 20 to be 4. In various other words, 4 is the largest variable that both numbers have actually in common. We deserve to see the by looking at the element factorizations of both numbers:


The blue numbers are the prime components of both numbers. To discover the GCF, simply determine the prime components that both numbers have in common and also multiply castle together.

Both number have usual prime determinants of 2 and also 2. 2 x 2 = 4. This describes how your mommy knew to reduced both cakes right into 4-square-inch pieces!

What is the GCF the 15 and also 27?

In this case, both numbers only have one typical factor, 3. The equipment is commonly written GCF (15,27) = 3.

What is the GCF the 18 and also 36?

GCF (18,36) = 2 x 3 = 6.

Find the GCF of 7 and 56.


In this case, among the numbers is prime and it is a variable of the various other number. GCF (7,56) = 7.

Find the GCF the 7 and 13.


The number 1 is no a prime number, but it is the GCF that 7 and also 13, which space both prime numbers.

GCF (7,13) = 1

Let’s briefly return to the cakes. Her mom uncovered that:

and that the GCF is 4, for this reason she need to divide the cakes right into 4-square-inch pieces. Look in ~ the number that room not component of the GCF:

The yellow number tell united state that there room 3 4-square-inch pieces in the little cake and also 5 4-square-inch piece in the big cake. A total of 8 4-square customs pieces renders sense, since 8×4=32, which equates to the cake size of 12 and also 20 square inches, since 12+20=32. 

Suppose 60 girls and also 48 boys desire to beat in a kickball tournament. What is the greatest number of teams that can be created that have actually the same ratio of girl to boys? How many girls and also boys would certainly each team have?

3 x 2 x 2 = 12 teams could be formed, every containing 5 girls and 2 x 2 = 4 boys.


The Least common Multiple

You’re craving hot dogs, so friend head come the store and pick increase a load of dogs and also a load of buns. Typically, a package of franks consists of 10, if a load of buns contains 8. This brings us to one of the good mathematical quandaries of ours time. After friend eat 8 dogs, you’ll have actually 2 left, however you’ll be the end of buns. You will do it need an additional pack the buns therefore the dog don’t walk to waste. Of course, after you eat those, you’ll have actually 6 buns and also no dogs. Off to the keep you’ll go, once again, and also the bicycle continues. 


In order to number out the warm dog problem, we need to uncover the Least usual Multiple (LCM) that buns and also dogs. We require the lowest number that is divisible by both the variety of dogs in a pack and buns in a pack. Once we find that number, us can number out how numerous packs of every to to buy so us don’t have any leftovers.

Let’s begin by listing out some multiples the dogs and also buns:


There space many common multiples of dogs and buns, yet you have the right to see the the LCM of warm dogs and also buns is 40. Other usual multiples room 80, 120, etc. Purchase 4 packs of warm dogs and also 5 packs of buns will ensure a dog for every bun. Hope you’re hungry!

Prime factorization can be used right here as well. Recognize the LCM this way is kind of opposing as when finding the GCF. Because that GCF, we desire the typical factors. For LCM, we desire the distinct factors. If a variable occurs in both numbers, we desire the highest power of the factor. Here goes!

To calculation the LCM, we first need the 5 indigenous factoring 10. Notice that 2 occurs as a factor of both 10 and also 8. Remember, we require the greatest power that 2:

The prime factorization of 10 is \(2\times 5 = 2^1\times 5\). The element factorization the 8 is \(2\times 2\times 2 = 2^3\).

The second number for our calculation is \(2^3\), because 3 is higher than \(1.5\times 2^3=5\times 8 = 40\), simply as we discovered previously.

LCM (10,8) = 40

What is the LCM that 15 and 27?

LCM (15,27) = \(5\times 3^3 = 5\times 27 = 135\).

What is the LCM of 18 and also 36?


The factorizations the both numbers contain 2 and 3 and the highest possible power the both of them is 2.

LCM (18,36) = \(2^2\times 3^2 = 4\times 9 = 36\). Notice that 36 is a many of 18, likewise the LCM.

Find the LCM that 7 and 56.


Again, notification one of the number is prime and it is a variable of the other number. LCM (7,56) = \(7\times 2^3=7\times 8 = 56\).

Find the LCM of 7 and also 13.


The LCM of 7 and 13, both element numbers, is just LCM(7,13) = 7 x 13 = 91.

Starting in ~ 8:00 a.m., a northbound train stops at a terminal every 12 minutes and also a southbound train stop at the exact same station every 20 minutes. When is the next time both trains will be stopped at the terminal at the very same time?


LCM (12, 20) = \(2^2\times 3\times 5= 4\times 3\times 5 = 60\). After ~ 60 min, or in ~ 9:00, is the following time both trains will certainly be in ~ the terminal at the exact same time.

See more: Crude Oil Is A Toxic Chemical That Is Oning, Oil Toxicity

There is one east-west train that stops at the terminal every 8 minutes. Once is the next time all 3 trains will certainly be quit at the terminal at the very same time?

LCM (12,20,8) = \(3\times 5\times 2^3 = 120\). After 120 minutes, or at 10:00, is the next time all three trains will be in ~ the terminal at the exact same time.

Final Thoughts! 

When trying out with factors and multiples, the GCF and also LCM regularly prove useful. Their skills can come in handy because that calculations, such as simplifying fractions. However, as we’ve seen, these expand our expertise of multiplication and also division, pushing united state to truly grasp what it method for a number to it is in a variable or a multiple, and enable us to make feeling of yes, really situations. The best component is, all you have to do to exercise is choose some numbers. We greatly practiced v two at a time, but you can uncover the GCF and LCM of any kind of group the numbers. Provide it a shot!