Is x a prime number? (2) y^2 = x (1) 2x/x^2 = 1

Question

Is x a prime number?

(2) y^2 = x
(1) 2x/x^2 = 1

sterling19 · Accepted Answer

I'm guessing there is a typo and that  y^2=x  is actually statement 1.

(1)  y^2=x     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     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 .

Robcarr65 · Answer

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.

sterling19 · Answer

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

Robcarr65 · Answer

Thank you. Careless mistake on my part.

nababorah0399 · Answer

Is x a prime number?

(2) y^2=x
(1) 2x/x^2 = 1

Statement 1 is sufficient- 2x/x^2=1.

CrackverbalGMAT · Answer

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.

rajthakkar · Answer

(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)

Bunuel · Answer

VERITAS PREP OFFICIAL SOLUTION

Correct 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 cross-multiply 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.

Celestial09 · Answer

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

KS15 · Answer

Bunuel-could you please help?

Statement 2: If we take x^2 to the opposite side, 2x=x^2 and x^2-2x=0
x(x-2)=0.Therefore, x=0 or 2. How can we determine?

Thanks

abhimahna · Answer

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.

stonecold · Answer

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

samriddhi1234 · Answer

One property of GMAT questions really saved me here - two statements in a DS will  NEVER  say the opposite thing, eg if statement A says x is not prime then B will  never  say that x is prime.

I dismissed statement A too early, thinking that as x is a perfect square so it must not be prime. But when it came to analysing B: x = 2 which is prime. So instead of picking D, I realised that y could be a square root. so B is the answer.

in case this helps anyone hehe

Is x a prime number? (2) y^2 = x (1) 2x/x^2 = 1

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GMAT Data Sufficiency (DS) Questions

Is x a prime number? (2) y^2 = x (1) 2x/x^2 = 1

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