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Is integer x prime? (1) x = | x | (2) x! = | x |

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Bunuel
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Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   10 Dec 2016, 06:33
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E

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63% (01:02) correct 37% (00:59) wrong based on 279 sessions
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Is integer x prime?

(1) x = | x |
(2) x! = | x |
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E
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prashantrchawla
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   10 Dec 2016, 09:06
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We need to find out whether x is prime or not ?
Option 1: x = | x |, All the positive values will satisfy this equation. Not sufficient.
Option 2: x! = | x |, For two values of x, i.e. 1 and 2 will satisfy this equation. Not sufficient
Taking both the options, will not satisfy this options. Hence answer is E. Hope I am right ?
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   10 Dec 2016, 09:37
Statement 1: x can be equal to |x| only for non-negative integers, but it does tell if x is prime or not

Statement 2: x!=|x|

Above condition is true for x=1,2

1 is not a prime number while 2 is a prime number => statement 2 is not sufficient

Combining both:

both conditions are satisfied when x=1,2 (same as statement 2)

So E is the correct answer

+1 Kudos if you like the post :)
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shikha.lakhani
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   23 Feb 2017, 05:13
what does x! mean? did not get the b condition
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   23 Feb 2017, 05:49
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shikha.lakhani wrote:
what does x! mean? did not get the b condition


Definition

The factorial of a non-negative integer \(n\), denoted by \(n!\), is the product of all positive integers less than or equal to \(n\).

For example: \(4!=1*2*3*4=24\).

Properties

  • Factorial of a negative number is undefined.
  • \(0!=1\), zero factorial is defined to equal 1.
  • \(n!=(n-1)!*n\), valid for \(n\geq{1}\).
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink] New post   23 Feb 2017, 06:58
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Is integer x prime?

(1) x = | x |
(2) x! = | x |

Prompt analysis
x is an integer

Super set
the answer will be either yes or no

Translation

In order to find the answer, we need:
1# exact value of x
2# any equation to find the value of x
3# any property to narrow down the value to 1

statement analysis
St 1: x = |x|. this will hold for any positive value of x. INSUFFICIENT
St 2: x! = |x|. this will hold for x = 1 and 2. INSUFFICIENT
St1 & St2: again both the condition is true for x = 1 and 2. INSUFFICIENT

Option E
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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink]
23 Feb 2017, 06:58
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Bunuel
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