If -x is a prime number, what is the value of x?

Question

(1) x^2 + 5x + 6 = 0
(2) x^2 + 3x + 2 = 0

stonecold · Answer

Given data => -x is a prime number.

Statement 1 => x^2 + 5x + 6 = 0
x => {-2,-3} 
Both are possible as -x would be 2 and 3 which are both prime.

Not sufficient.

Statment 2 => x^2 + 3x + 2 = 0 
x=>{-1,-2}
Here x cannot be -1 as 1 is not prime.

Hence x must be -2

Sufficient.

Hence B.

akshayk · Answer

1) (x+3)(x+2)=0
Insufficient. 2 values of x.

2) (x+1)(x+2)=0
x = 2. Sufficient.

B.

sashiim20 · Answer

(1)  x^2 + 5x + 6 = 0 
 x^2+3x+2x+6 = 0 
 x(x+3)+2(x+3) = 0 
 (x+3)(x+2) = 0 
 x = -2, -3 
(1) has 2 values of x. I is Not Sufficient.

(2)  x^2 + 3x + 2 = 0 
 x^2+2x+x+2 = 0 
 x(x+2)+1(x+2) = 0 
 (x+1)(x+2) = 0 
 x = -2,-1.

Given, x is prime number. Therefore x could only be 2. (1 is not prime)

(2) has only 1 value of x. Hence II is Sufficient. Answer (B)...

Luckisnoexcuse · Answer

We know x is a negative of prime number

(1) On solving  x^2 + 5x + 6 = 0  we get x as -3 and -2 . Not sufficient

(2) On solving  x^2 + 3x + 2 = 0  we get x as -2 and -1 .Sufficient as 1 is not a prime number

Hence B

shashankism · Answer

Lets start checking the options 1 and 2 
1. x^2 + 5x + 6 = 0
-> (x+3)(x+2) = 0 
-> x = -3,-2

Prime numbers 3,2 NOT SUFFICIENT

2. x^2 + 3x + 2 = 0
-> (x+2)(x+1) = 0 
-> x = -2, -1 
Prime Number 2. SUFFICIENT

Answer B.

Prep Toolkit