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For which of the following values of a does (a + 4)(a + 3)(a + 2)(a +

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V
Joined: 02 Sep 2009
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Kudos [?]: 128979 [0], given: 12185

For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + [#permalink]

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New post 19 Dec 2016, 05:29
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A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

67% (01:59) correct 33% (01:53) wrong based on 117 sessions

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Kudos [?]: 128979 [0], given: 12185

Senior Manager
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B
Joined: 13 Oct 2016
Posts: 367

Kudos [?]: 395 [0], given: 40

GPA: 3.98
Re: For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + [#permalink]

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New post 19 Dec 2016, 06:32
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Bunuel wrote:
For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + 1) = (a + 1)! ?

A. 9
B. 8
C. 7
D. 6
E. 5


Or (a + 4)(a + 3)(a + 2) = a!

A) 9 + 4 will give us 13 but 9! does not have 13 as a factor. Impossible
B) 8 + 3 will give us 11 but 8! does not have 11 as a factor. Impossible.
C) Same logic 7 + 4 = 11 and 7! does not have 11 as it’s prime factor.
D) 10*9*8 = 720 = 6!
E) 5+2 will give us 7 and 5! Does not have 7 as its prime factor

Answer D

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Re: For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + [#permalink]

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New post 19 Dec 2016, 09:29
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vitaliyGMAT wrote:
(a + 4)(a + 3)(a + 2) = a!


Perfect solution...

At this point one can start testing the option...

When \(a = 6\)

\((a + 4)(a + 3)(a + 2) = a!\)

Or, \(10*9*8 = 6!\)

Hence, correct answer must be (D) 6
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Kudos [?]: 1087 [1], given: 325

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Kudos [?]: 18 [0], given: 46

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Re: For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + [#permalink]

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New post 20 Dec 2016, 01:29
First, using the factorials rule we should express (a+1)!=(a+1)a!
Second, (a+4)(a+3)(a+2)(a+1)=(a+1)a! divide both sides by (a+1)
(a+4)(a+3)(a+2)=a!
(a+4)(a+3)(a+2)/a!=1
After substitution of all offered options it is clear that only 6 is possible, thus correct answer is D.

Kudos [?]: 18 [0], given: 46

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Re: For which of the following values of a does (a + 4)(a + 3)(a + 2)(a + [#permalink]

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New post 18 Aug 2017, 09:15
Used substitution! Started from Option E. Found a = 6.
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Consistency is the Key

Kudos [?]: 15 [0], given: 22

Re: For which of the following values of a does (a + 4)(a + 3)(a + 2)(a +   [#permalink] 18 Aug 2017, 09:15
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