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# The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM

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Joined: 27 May 2014
Posts: 525
GMAT 1: 730 Q49 V41
The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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23 Jan 2017, 11:23
1
6
00:00

Difficulty:

85% (hard)

Question Stats:

51% (02:22) correct 49% (02:50) wrong based on 127 sessions

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The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM is 2^3 × 3^2 × 5 × 103 × 107,
then the number ‘N’ is:

(A) 2^2 × 3^2 × 7
(B) 2^2 × 3^3 × 103
(C) 2^2 × 3^2 × 5
(D) 2^2 × 3 × 5
(E) None of these

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Joined: 13 Oct 2016
Posts: 367
GPA: 3.98
Re: The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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23 Jan 2017, 12:08
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2
saswata4s wrote:
The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM is 2^3 × 3^2 × 5 × 103 × 107,
then the number ‘N’ is:

(A) 2^2 × 3^2 × 7
(B) 2^2 × 3^3 × 103
(C) 2^2 × 3^2 × 5
(D) 2^2 × 3 × 5
(E) None of these

$$LCM (2472, 1284, N) = 2^3 × 3^2 × 5 × 103 × 107$$

$$2472 = 2^3*3*103$$

$$1284 = 2^2*3*107$$

In order to produce required LCM our N should have 3^2 and 5, because none of the 2472 and 1284 have them.

Only option that fits is C.
Intern
Joined: 25 Sep 2017
Posts: 3
The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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Updated on: 22 Oct 2017, 08:48
HCF = 12 = 2^2 x 3
LCM = 2^3 × 3^2 × 5 × 103 × 107

2472 = 2^3 x 3 x 103
1284 = 2^2 x 3 x 107

Since we know, Product of LCM and HCF = Product of Numbers

(2^2 x 3) x (2^3 x 3^2 x 5 x 103 x 107) = (2^3 x 3 x 103) x ( 2^2 x 3 x 107) x N

2^5 x 3^3 x 5 = 2^5 x 3^2 x N

3 x 5 = N

So N is 3*5 and answer is E (None of the Above)

Edited: And, I realised that below formula is applicable only when there are two numbers. If there are more than two numbers then their HCF should be 1(they should be prime numbers).
Product of LCM and HCF = Product of Numbers

Hence above solution is incorrect.

Originally posted by ramanbajwa2003 on 03 Oct 2017, 05:26.
Last edited by ramanbajwa2003 on 22 Oct 2017, 08:48, edited 1 time in total.
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Joined: 08 Nov 2015
Posts: 12
Re: The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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21 Oct 2017, 04:33
ramanbajwa2003 wrote:
HCF = 12 = 2^2 x 3
LCM = 2^3 × 3^2 × 5 × 103 × 107

2472 = 2^3 x 3 x 103
1284 = 2^2 x 3 x 107

Since we know, Product of LCM and HCF = Product of Numbers

(2^2 x 3) x (2^3 x 3^2 x 5 x 103 x 107) = (2^3 x 3 x 103) x ( 2^2 x 3 x 107) x N

2^5 x 3^3 x 5 = 2^5 x 3^2 x N

3 x 5 = N

So N is 3*5 and answer is E (None of the Above)

Hi Raman,

If N is 15, then how can it have HCF as 12?
Director
Joined: 31 Jul 2017
Posts: 517
Location: Malaysia
GMAT 1: 700 Q50 V33
GPA: 3.95
WE: Consulting (Energy and Utilities)
Re: The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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21 Oct 2017, 06:21
ramanbajwa2003 wrote:
HCF = 12 = 2^2 x 3
LCM = 2^3 × 3^2 × 5 × 103 × 107

2472 = 2^3 x 3 x 103
1284 = 2^2 x 3 x 107

Since we know, Product of LCM and HCF = Product of Numbers

(2^2 x 3) x (2^3 x 3^2 x 5 x 103 x 107) = (2^3 x 3 x 103) x ( 2^2 x 3 x 107) x N

2^5 x 3^3 x 5 = 2^5 x 3^2 x N

3 x 5 = N

So N is 3*5 and answer is E (None of the Above)

We cannot use this logic as:

Product of two numbers = Product of their H.C.F. and L.C.M.
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Intern
Joined: 18 Nov 2017
Posts: 43
Re: The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM  [#permalink]

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25 Jun 2018, 00:50
saswata4s wrote:
The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM is 2^3 × 3^2 × 5 × 103 × 107,
then the number ‘N’ is:

(A) 2^2 × 3^2 × 7
(B) 2^2 × 3^3 × 103
(C) 2^2 × 3^2 × 5
(D) 2^2 × 3 × 5
(E) None of these

Hi Bunuel,

Thanks!
Re: The HCF of 2472, 1284 and a third number ‘N’ is 12. If their LCM &nbs [#permalink] 25 Jun 2018, 00:50
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