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Is x a prime number? [#permalink]
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16 Feb 2015, 06:54
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Re: Is x a prime number? [#permalink]
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16 Feb 2015, 07:56
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I'm guessing there is a typo and that \(y^2=x\) is actually statement 1.
(1) \(y^2=x\) [Insufficient] We are not told that y is an integer. If y is an integer, then x is not prime. Otherwise, y could be the square root of a prime such as \(\sqrt{2}\) (2) \(2x/x^2 = 1\) [Sufficient] From this statement, we can see that x is not zero. Multiplying both sides by \(x^2\), we get \(2x = x^2\). Dividing both sides by x, we are left with x = 2, which is a prime number.
The correct answer is B.



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Re: Is x a prime number? [#permalink]
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16 Feb 2015, 09:27
My answer was C. Neither statement is sufficient: In stmt 1, "y" can be 0,1, or the square root of a prime as stated above. Multiple possibilities, not sufficient In stmt 2, "x" can be 1 or 2 and (2x / x^2) will equal 1. Multiple possibilities, not sufficient.
The problem never specified that x or y must be integers.



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Re: Is x a prime number? [#permalink]
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16 Feb 2015, 11:59
Robcarr65 wrote: In stmt 2, "x" can be 1 or 2 and (2x / x^2) will equal 1. x cannot be 1 as \((2*1)/(1^2) = 2/1 = 2\) This may be confusing if you aren't familiar with the ^ sign. It means "raised to the power of". So 2^3 = \(2^3\) = 8



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Re: Is x a prime number? [#permalink]
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16 Feb 2015, 14:06
sterling19 wrote: Robcarr65 wrote: In stmt 2, "x" can be 1 or 2 and (2x / x^2) will equal 1. x cannot be 1 as \((2*1)/(1^2) = 2/1 = 2\) This may be confusing if you aren't familiar with the ^ sign. It means "raised to the power of". So 2^3 = \(2^3\) = 8 Thank you. Careless mistake on my part.



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Re: Is x a prime number? [#permalink]
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17 Feb 2015, 03:17
Is x a prime number?
(2) y^2=x (1) 2x/x^2 = 1
Statement 1 is sufficient 2x/x^2=1.



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Re: Is x a prime number? [#permalink]
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19 Feb 2015, 23:39
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Statement 1 is insufficient: y^2=x If y is an integer then x is not prime. If y is not an integer like sqrt2,sqrt3…. then x is prime. So not sufficient. Statement 2 is sufficient: 2/x=1 So x is 2. Which is prime. So answer is B.
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Is x a prime number? [#permalink]
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20 Feb 2015, 01:12
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(1) it states that x is positive but doesn't provide any detail of x being prime
Not Sufficient
(2) 2x/x^2=1 x can hold only one value I.e. 2 as x can not be 0
Sufficient
IMO (B)



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Re: Is x a prime number? [#permalink]
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22 Feb 2015, 11:17
Bunuel wrote: Is x a prime number?
(2) y^2=x (1) 2x/x^2 = 1
Kudos for a correct solution. VERITAS PREP OFFICIAL SOLUTIONCorrect Answer: B I. y could be 1, giving us a NO answer to the question (since 1 is not prime), or it could be (2)−−−√, giving us a YES answer to the question (since 2 is prime). Insufficient. II. If you crossmultiply this equation, you'll get 2x = x². There are two solutions to this equation 0 and 2, but we can rule out 0, because that would put 0 in the denominator of the fraction in the original form of the equation, and putting 0 in the denominator is not allowed; it is undefined. Therefore, x must be 2, a prime, giving us a YES in answer to the question. Sufficient.
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Re: Is x a prime number? [#permalink]
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06 Aug 2016, 15:40
Bunuel wrote: Bunuel wrote: Is x a prime number?
(2) y^2=x (1) 2x/x^2 = 1
Kudos for a correct solution. VERITAS PREP OFFICIAL SOLUTIONCorrect Answer: B I. y could be 1, giving us a NO answer to the question (since 1 is not prime), or it could be (2)−−−√, giving us a YES answer to the question (since 2 is prime). Insufficient. II. If you crossmultiply this equation, you'll get 2x = x². There are two solutions to this equation 0 and 2, but we can rule out 0, because that would put 0 in the denominator of the fraction in the original form of the equation, and putting 0 in the denominator is not allowed; it is undefined. Therefore, x must be 2, a prime, giving us a YES in answer to the question. Sufficient. Hi! Just a small query please st1) doesnt matter at all y could be anything.......... ok? st2) can x as a variable be reduced.. as its an equation rather inequality.. and hence coming up B as an answer... please help in this.. thanks



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Re: Is x a prime number? [#permalink]
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07 Aug 2016, 09:19
Bunuel wrote: Is x a prime number?
(2) y^2=x (1) 2x/x^2 = 1
Kudos for a correct solution. Bunuelcould you please help? Statement 2: If we take x^2 to the opposite side, 2x=x^2 and x^22x=0 x(x2)=0.Therefore, x=0 or 2. How can we determine? Thanks



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Re: Is x a prime number? [#permalink]
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07 Aug 2016, 09:34
KS15 wrote: Bunuel wrote: Is x a prime number?
(2) y^2=x (1) 2x/x^2 = 1
Kudos for a correct solution. Bunuelcould you please help? Statement 2: If we take x^2 to the opposite side, 2x=x^2 and x^22x=0 x(x2)=0.Therefore, x=0 or 2. How can we determine? Thanks Once you have got the value of x as 0 and 2, you need to put the value in the actual statement to see if it works. So, if you put x=0, you will have 0/0 form, which is NOT DEFINED. Hence, x cannot be 0, thus x=2 only. Hence, sufficient.
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Re: Is x a prime number? [#permalink]
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16 Oct 2016, 03:32
We need to get if x is prime or not statement 1 => x=y^2 If y is an integer then x wont be prime ( Primes can never be factorised) Else if y=√2 then x=2 => Prime Hence since no clue of y is given => Not suff Statement 2 => 2x/x^2=1 here x can never be 0 as something /0 => not defined hence x^2=2x=> x=2 which is a prime number Therefore suff Hence B
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Re: Is x a prime number? [#permalink]
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