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# 3 Deadly Mistakes you must avoid in LCM-GCD Questions

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This is a great post.
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EgmatQuantExpert wrote:
Product of all integers in the set = GCD * LCM

Hi Harsh
is this statement applicable only in a case of only two integers? so GCD(M, N) × LCM(M, N) = M × N,

how that's working for example for the following set {2,4,8}
their product = 64
whilst GCD * LCM = 2 * 16 = 32
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Thank you for this post.

To find the GCD, I want to know if the below process always gives the correct answer.

1) write in the form of Prime Factors.
Say 12,18
12 - 2^2 x 3^1
18 - 2^1 x 3^2

2) Taking the factors common between them
Common - 2^1 x 3^1 = 6
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cbh wrote:
EgmatQuantExpert wrote:
Product of all integers in the set = GCD * LCM

Hi Harsh
is this statement applicable only in a case of only two integers? so GCD(M, N) × LCM(M, N) = M × N,

how that's working for example for the following set {2,4,8}
their product = 64
whilst GCD * LCM = 2 * 16 = 32

Hey cbh,

Yes the formula GCD(M,N) * LCM(M,N) = M x N, is applicable only for two variables.

We can create similar formulas for 3 or more variables, but that would be really out of scope for GMAT exam and I would not bother learning another new formula, which might not be used at all.

Regards,
Saquib
e-GMAT Quant Expert

Originally posted by EgmatQuantExpert on 29 Dec 2017, 23:27.
Last edited by EgmatQuantExpert on 07 Aug 2018, 00:57, edited 1 time in total.
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siddharthselvamohan wrote:
Thank you for this post.

To find the GCD, I want to know if the below process always gives the correct answer.

1) write in the form of Prime Factors.
Say 12,18
12 - 2^2 x 3^1
18 - 2^1 x 3^2

2) Taking the factors common between them
Common - 2^1 x 3^1 = 6

Hey Siddharth,

Yes, the method that you have used will always give you the correct answer.

Regards,
Saquib
e-GMAT Quant Expert
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Hey everyone,

We have added a few practice question on the application of LCM and GCD

Practice Question #1
Practice Question #2
Practice Question #3

Regards,
Tamal
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Hey everyone,

The official answers to all the practice questions have been posted.

Regards,
Tamal
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Dear Students,

You can go through the article from this Common Mistakes One Must Avoid in Remainders

Stay tuned for more articles.

Happy learning

Regards,
Sandeep
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Thank you! Found this very helpful
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Such a helpful post. A much needed one, infact. Thanks!
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Dear Students,

We have added a new article to discuss two interesting applications of Remainders.

You can go through the article from this Interesting Applications of Remainders

Stay tuned for more articles.

Happy learning

Regards,
Tamal
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Dear Students,

We have added a new article to discuss the variations in factorial manipulation.

You can go through the article from this Variations in Factorial Manipulation

Stay tuned for more articles.

Happy learning

Regards,
Sandeep.
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Hey Everyone,

We have posted the official solutions to all the practice questions.

Regards,
Sandeep
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Hey Everyone,

We've added 4 new practice questions in which you can apply your learnings of Number Properties.

Exercise Questions

Question 1

Question 2

Question 3

Question 4

Detailed solutions will be posted soon.

Happy Learning!
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