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

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Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink]
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]
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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]
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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
Re: Is integer x prime? (1) x = | x | (2) x! = | x | [#permalink]
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