bkk145 wrote:
Kiski wrote:
M and N are both nonzero integers. Is M/N a prime number?
(1) |M|=–M
(2) |N|=N
I dont have the OA on this.Can someone please verify my approach .I am weak in modulus and have only recently started to look at this topic :
from 1 : since |M| has to be +ve ,and |M| = - M ,we know M is -ve. Insuff,no info on N
from 2 : |N| = N => N can be =+ve or -ve.Insuff .No info on M
1 and 2 together : M/N can be +ve or -ve (assuming prime no.s are positive) therefore E.
First, I am quite sure that negative number can't be prime.
For this question, I get E.
For M/N to be a prime, M must equal a prime and N equals 1
(1) |M| = -M
if M>0, M = -M
If M<0> M=M
So M can be either negative or positive, but we still don't know N.
INSUFFICIENT
(2) |N|=N
if N>0, N=N
if N<0, N=-N
Don't know M.
INSUFFICIENT
Together, I still can't draw any conclusion.
1. M
must be negative. Since |M| must be a positive then - M must be positive as well. The only way for - M to be positive is if M is negative itself.
2. If a negative number cannot be prime than the answer would be C. M/N is 100% for certain a negative number in this problem. If negatives cannot be primes and it's asking if M/N is prime we can answer this 100% no. So if the GMAT takes the stance that there cannot be negative primes the answer would be C.
3. "for M/N to be a prime, M must equal a prime and N must equal 1" this isn't true at all. 14/2 = 7 which is a prime. 33/3 = 11 which is a prime. There are tons of ways to divide two numbers and come up with a prime. The only way you can get a prime number through
multiplication is if one number is prime and the other is one (this is the very definition of a prime number).